Daniels is a narcotics lieutenant in season one and the shift commander for Detectives Kima Greggs, Ellis Carver and Thomas "Herc" Hauk. Daniels' commanding officer is Major Raymond Foerster.
When Jimmy McNulty prompts Judge Phelan to start asking questions about the Barksdale Organization, Major Foerster comes to Daniels for more information. He wasn't able to offer much as the narcotics division were unaware of Avon Barksdale. He had Greggs write a report and, soon after, Daniels is given command of the Barksdale Detail. He nominates Greggs as lead detective and describes her as the best he had to Foerster. He meets with Deputy Commissioner Burrell who tells him the case should be made with buy busts in a fast, straightforward investigation.
Daniels discusses his new assignment with his ambitious wife Marla. They worry that it might slow his progression and he promises that he will run the investigation per the wishes of the higher-ups. Marla's own ambitions drive her to pursue a career in politics and Cedric attends political fundraisers with her. At one such function he finds himself hiding with the politicians' drivers in the kitchen. There, he meets Senator Clay Davis' driver Damian "Day-Day" Price, later discovered to be a bag man involved with the Barksdales.
Daniels has a difficult relationship with the insubordinate McNulty that begins at their first meeting. Foerster and Burrell both warn Daniels that McNulty is responsible for Phelan's sudden interest. For his part, McNulty is warned by Bunk Moreland that Daniels is a career officer and next in line for his own district as soon as a position with a Major's rank opened up. McNulty's FBI contact also alerts him that Daniels has several hundred thousand dollars of questionable liquid assets; it is later implied that these were picked up during Daniels' tenure in the poorly-supervised Eastern district. Daniels initially tries to follow Burrell's advice that the operation should be fast and simple. He shoots down McNulty's suggestions of a surveillance operation at their first meeting.
Daniels also has difficulties with several other detectives on the detail. He is initially assigned "humps" - detectives that other districts wanted to remove. Augustus Polk, Patrick Mahon and Lester Freamon appeared to be aging detectives happy to see out their careers. Mahon is injured by Bodie during a raid and takes early retirement; following this, his partner Polk takes to drinking more heavily and misses several days' work. Daniels insists that Polk either clean himself up or sign off sick; Polk opts for the latter. Freamon proves to be quietly capable and a huge asset to Daniels's detail.
Roland Pryzbylewski is a trigger happy detective who had once shot up his own patrol car before he is assigned to Daniels's detail. Daniels is able to convince Prez's commanding officer, Lieutenant Walter Cantrell, to balance taking the difficult officer out of his hands by assigning him the promising Leander Sydnor. Prez continues his self-destructive behaviour, attending an unsanctioned, drunken late-night raid on the Barksdale tower operations with Herc and Carver. Prez injures a young boy and Daniels is left to deal with the consequences. He stands by Prez despite his history of problems and defends him to his superiors. In the process he gains the respect of Prez's father-in-law, Major Valchek. Under Daniels's supervision and Freamon's tutelage Prez develops into an effective data analyst. Sydnor is also a valuable asset to the Daniels detail, performing undercover work and gelling well with the dependable Freamon.
Herc and Carver continue to be problematic for Daniels. He suspects them of skimming when the drug money they turn in to evidence does not match a reported amount. He remains loyal to his men, leniently giving them one day to return it rather than turning them in immediately.
As the investigation progresses, Daniels's attitude towards the case changed. He risks his career several times in order to protect the case. When Major Bill Rawls wants to issue a murder warrant for D'Angelo Barksdale based on flimsy evidence, the Barksdale detail is dismayed, since arresting D'Angelo would tip off Avon to the investigation. McNulty and Greggs plead with Daniels to fight for their case. Daniels appeals to Rawls and then to Foerster to hold off on arresting D'Angelo, without success. Finally Daniels bypasses the chain of command and meets directly with Burrell and an angry Rawls. After a heated argument, Daniels manages to persuade Burrell to delay the warrants.
Freamon begins to investigate Barksdale's money trail and found campaign contributions to Baltimore political figures. Daniels's team arrest his acquaintance, Day-Day, the senator's driver, collecting cash from the Barksdale crew. Rather than seizing the money, Daniels' superiors force him to return the money with no further investigation to avoid raising the senator's ire. When Burrell, in order to shut the case down, threatens to reveal the source of Daniels's liquid assets, Daniels calls his Burrell's bluff, pointing out the Deputy's fear of the bad press that would result in Daniels's past misdeeds coming to light. Daniels also is able to figure that Burrell is using Carver as a mole.
Over the course of the investigation, Daniels works closely with Assistant State's Attorney Rhonda Pearlman. She proves instrumental in using her judicial connections to provide Daniels with the warrants and affidavits needed for his teams surveillance efforts.
The Barksdale investigation ends with the arrests of Avon and D'Angelo, along with soldier Wee-Bey Brice and several other members of the organization. Convictions are secured against all participants and Wee-Bey confesses to several unsolved homicides to prevent fallout reaching other members of the organization. The result is unsatisfying for Daniels because Avon's conviction is for minor offences and Stringer Bell escapes uncharged to continue the organization's drug trade. Much better results are within Daniels's grasp when his team convinced D'Angelo to testify against the Barksdale organization. However, D'Angelo's mother Brianna talks him out of this course and he ends up taking a twenty-year sentence for his family.
Daniels's work on the Barksdale case certainly hurts his career; at the end of the first season, he is seen exchanging pleasantries with a newly minted major, a position that he had been on the fast track for. However, he has won the respect of his unit for a dedication to their cases, which surpasses that of their other commanding officers.
With the dissolution of the Barksdale detail, Daniels is reassigned to evidence control. He is given the post for defying Burrell, despite the investigation producing several arrests. Trapped in what seemed to be a dead-end job, Daniels contemplates quitting to become a lawyer, making use of his law degree, but reconsiders when Valchek insists (on Prez's recommendation) that Daniels be given command of a special detail to investigate union leader Frank Sobotka. Daniels realizes Valchek had asked for him personally in exchange for offering Burrell political support and uses this fact to leverage several promises from Burrell. Daniels stands his ground even though Burrell has the FBI file on Daniels's unexplained income. Daniels later confides to Marla that Burrell "knew," confirming that the allegations against Daniels are accurate. Daniels insists on picking his own detectives this time and forces Burrell to agree that if the investigation is successful then Daniels would become commander of a permanent unit.
Daniels's detail initially consists of Prez, Greggs and Herc. Rhonda Pearlman again acts as Daniels's courthouse liaison. At Herc's insistence, Daniels allows Carver the chance to rejoin the team despite his previous treachery (on the condition that Carver's promotion to sergeant will be in name only as Daniels feels Carver had not earned his stripes). Daniels campaigns for McNulty to rejoin the team but was denied by a vengeful Rawls. Daniels is able to convince Rawls to let him have Freamon, who had been assigned to homicide after the Barksdale detail. Sydnor has returned to his district and cannot be detailed. Daniels's detail works closely with Bunk Moreland, who is investigating multiple homicides at the docks, and Officer Beatrice Russell, detailed to Bunk's investigation from the Port Authority. Russell blossoms into a capable investigator with Daniels's team and is instrumental in coming up with the idea of cloning the ports computers to monitor smuggling. Daniels finally persuades Rawls to let McNulty return by agreeing to take on Rawls's murders from the docks.
While the investigation progresses, Cedric begins to have personal difficulties with wife due to his career decisions. Eventually, they begin to sleep in different rooms of their home.
The investigation progresses and the detail links Sobotka's union to a smuggling operation run by a mysterious figure called "The Greek". Sobotka's nephew Nick is proven to be involved in drug dealing and Sobtoka's son Ziggy is arrested for killing the Greek's fence George "Double G" Glekas. Daniels's detail is not informed of Ziggy's arrest until after Ziggy gives a signed confession to Jay Landsman, and this gives The Greeks time to clear out the warehouse. Valchek becomes disillusioned with Daniels when he learns that the focus was shifting away from Sobotka onto "The Greek" and he involves the FBI. Valchek insults the detail and Prez in a heated meeting and Daniels was forced to once again defend Prez after he punches Valchek. Daniels quickly collects statements from everyone present and convinces Valchek that it would be best to accept an apology from Prez.
With the wealth of evidence collected against Sobotka, he is arrested along with several other people identified by the team. The warrant for Double G reveals his empty shop and warehouse with all evidence disposed of. Daniels's people noticedthe bloodstain from the shooting and he goes to violent crimes to find out what had happened. Daniels is upset that Landsman had not realized the significance of the murder and told him of Ziggy's arrest. With several of Sobotka's family in jeopardy, Daniels's team convince him to act as an informant on "The Greek" and arranged for him to return with a lawyer the next day. Sobotka is murdered before the detail can take his testimony. "The Greek" himself escapes before the detail can locate him. The investigation is disappointing for the detail but deemed a tremendous success for the department. Bunk and Freamon secure evidence that solved the homicides, but the suspect involved has already been killed off by the Greek, so no conviction is made. Several prominent East-side drug figures are arrested, including "White" Mike McArdle, along with some of The Greek's men including Sergei Malatov and Eton Ben-Eleazer. Daniels is seen to have delivered on his promises and is once more in the department's good books.
Daniels's success in the Sobotka investigation means Burrell has to honor his promise to let Daniels form a permanent Major Case Unit. He retains McNulty, Greggs, Freamon, and Prez from the Sobotka unit. With Herc and Carver having departed the unit, their positions are filled by Sydnor and a new recruit, Caroline Massey. The detail returns to investigating the Barksdale organization and their association with Proposition Joe, an East Side drug kingpin with links to "The Greek" from the Sobotka investigation.
Cedric separates from Marla, partly because of her dissatisfaction at his failure to progress in the ranks. He finds that her attempt to enter politics after their separation further hinders his climb through the ranks, as she is running in opposition to a close ally of the mayor's. Nonetheless, he continues to support her through her political career, attending functions in uniform and acting the part of a devoted husband. After his separation from his wife, Cedric briefly lives out of the detail office, then, after moving into a bachelor apartment, starts a relationship with Pearlman. Cedric remains skeptical about making the relationship between him and Pearlman public as he is still appearing as Marla's husband in order to help promote her bid for city council. Daniels claims that it will look bad for Marla's political career for him to be seen separated from her with a white woman.
Throughout the season, he gets commended several times throughout the department due to his good police work, including from Rawls, Major Colvin, and Burrell, amongst other commanding officers. This, however, is not enough for Daniels, whose promotion to major is being held up due to Marla's political conflicts. Daniels also feels that Burrell is purposefully holding him back due to past incidents. Daniels becomes even more angered when McNulty goes around the chain of command to Colvin, and has the Major Case targets changed back to Stringer Bell and Avon Barksdale. This earns McNulty Daniels's wrath as he makes clear that McNulty is done with the MCU when Stringer is arrested. At the end of season three, Stringer is killed but Avon is rearrested thanks to a tipoff given from Stringer to Major Colvin. When Colvin is forced to retire from the department due to his "Hamsterdam" experiment, Daniels is promoted to Colvin's old post as Major for the Western District, as Mayor Royce throws support behind Marla.
Daniels is given the post of Western district commander with Dennis Mello acting as his administrative lieutenant. Lieutenant Jimmy Asher replaces him as commander of the major case unit even though Lester Freamon is the unit's true leader. Daniels tries to convince McNulty into returning to detective work but has little success. At the same time, Daniels realizes that on a personal level, McNulty was better off in patrol.
Kima meets with Daniels to discuss a transfer after Rawls replaces Asher with the abrasive Lieutenant Charles Marimow. Daniels suggest a move to homicide, and successfully meets with Rawls to facilitate the transfer.
After finding out that his student Randy Wagstaff knows information about Curtis “Lex” Anderson's murder, Prez (now a schoolteacher) meets with Daniels. Daniels suggests Ellis Carver as the person Prez should consult about the matter. Daniels questions Prez’s interest and Prez tells him he cares about Randy because he is one of his students.
Following the mayoral election, Daniels attends a COMSTAT meeting chaired by Rawls and Burrell. He tells his commanders that the homicide rate has dropped while other felony rates have risen. Primary victor Carcetti arrives to observe the meeting, later discussing the possibility of removing Burrell from commissioner, and possibly replacing him. However, he is warned that he would not be able due to racial issues. In the meeting, Carcetti observes that Daniels is more interested in quality felony arrests than statistical reductions on crime.
Carcetti next encounters Daniels while riding along with some Baltimore police officers who are called to a shooting. Daniels is the duty officer and is proficient in controlling the crime scene. Carcetti is impressed and learns from his accompanying officers that Daniels is more respected than most other commanding officers in the department. Carcetti invites Daniels to lunch and offers him a promotion to Colonel commanding the Criminal Investigations Division (CID) under Rawls. Daniels was officially promoted at the same ceremony as Major Stanislaus Valchek. Commissioner Burrell, becoming suspicious of the recent change of rank in the department, starts wondering about his future.
Burrell is especially worried about Daniels's promotion because he realizes Carcetti wants to fire him but needs an African American replacement in a majority-black city like Baltimore to do so. As Daniels suddenly rose in rank in going from Shift Lieutenant to CID colonel in just over one year, earned the mayor's favor through his policing strategies, and is African-American, Burrell sees Daniels as Carcetti's in-house choice of replacement. State Senator Clay Davis and Burrell are both wary of Daniels and convince the city council president Nerese Campbell that he is not a good candidate for police commissioner. They tell Campbell that he cares more about serving Carcetti than the city's African American community and that he is less the saint he pretends to be. This implies that Burrell is willing to revisit the excessive income charges from Daniels's days in the Eastern District's Drug Enforcement Unit to prevent Daniels from getting his chair as commissioner.
As CID colonel, Daniels clears Herc of a racial profiling incident and then assists Lester Freamon in building a case against the Stanfield Organization. Freamon discovers evidence of dead bodies in abandoned row houses and asks Daniels for more manpower for a citywide search. Daniels gives Freamon more patrolmen and the city's homicide rate increases dramatically with the discovery of 22 concealed bodies killed by the Stanfield Organization. During this time, it is pointed out to Rawls by Valchek that Daniels is likely to become the department's next commissioner. Daniels transfers McNulty back into the major crimes unit from Western patrol, with the unit again refocused on Marlo Stanfield. As the season ends, Rawls believes that Daniels will be moved up the ladder even further while Burrell and Davis conspire to keep Daniels from getting the commissioner's post.
Daniels is outraged when Carcetti decides to close the major crimes unit due to budgetary problems after over a year of investigative work into the vacant house murders, the Stanfield Organization and corruption linked to Senator Clay Davis. He discusses it with his domestic partner, Assistant State's Attorney Rhonda Pearlman, and they approach State's Attorney Rupert Bond together. Bond and Daniels arrange a meeting with Carcetti to appeal the decision but Carcetti has little time for them. Bond is able to convince Carcetti to allow a two-man detail for the Davis case. Daniels is outraged that the corruption charge has been given priority over the murders, saying "So one thieving politician trumps 22 dead bodies. Good to know." Daniels reluctantly reassigns Kima Greggs and Jimmy McNulty to homicide and keeps Lester Freamon and Leander Sydnor for the Davis detail.
Carcetti finally accrues the political capital he needs to fire Commissioner Ervin Burrell when Burrell delivers false crime statistics to Carcetti. Carcetti plans to fire Burrell and temporarily promote Rawls to acting commissioner with Daniels serving as Deputy Commissioner of Operations to prepare him to take over as commissioner. Carcetti leaks the story to The Baltimore Sun to gauge reaction to Daniels. The story runs with a quote invented by Scott Templeton and attributed to a city hall source. The quote falsely implicates Daniels in causing Burrell's departure.
Daniels discusses the story with Pearlman and while she is ecstatic he is concerned about Templeton’s quote. Daniels meets with his ex-wife Marla to discuss Burrell’s potential reaction to the story. They are both worried that Burrell will reveal evidence of corruption from Daniels’s past. Marla suggests that Burrell will use what he knows about Daniels to try to retain his position as commissioner. Marla suggests that Daniels approach Burrell and promise not to take the commissioner post. Daniels thinks that Burrell might not have any more than assets investigations but Marla reminds him that his past has already cost their marriage, which was a high enough price, and that rumor will be enough to prevent him from becoming commissioner.
Daniels approaches Burrell to plead his innocence but is met with the silent treatment. City Council President Nerese Campbell convinces Burrell to leave quietly in exchange for a comfortable replacement position. Carcetti holds a press conference to announce the promotions.
During the final episode Daniels is promoted to Commissioner after the homeless killings and the case of the murders in the abandoned houses is solved. However, after refusing to "juke the stats" and Campbell's threats of revealing Burrell's dossier, he resigns from the force. His last act as police commissioner is to confer a set of promotions, including that of Ellis Carver to Lieutenant. In the final flash-forward montage, Daniels is shown practicing as a criminal defense lawyer before Pearlman as a newly commissioned judge.
Lance Reddick was cast in the role after auditioning for the parts of Bunk Moreland and Bubbles. He was told that they were looking for "a name" to fill the Daniels role. Reddick has described the character as serious, intense and committed.