Daniels is the son of Judy, who worked at the New York Public Library, and Aaron Daniels, who was president of ABC Radio Network. He has stated that he became interested in comedy by watching Monty Python's Flying Circus as a child, as well as by reading books by humorist S. J. Perelman at age 11. His first joke was a Carnac the Magnificent joke for his father which was later used for The Office episode, "The Dundies." Daniels attended Phillips Exeter Academy and then Harvard University where he wrote for the Harvard Lampoon with Conan O'Brien. After graduating in 1984, the two accepted jobs at Not Necessarily the News, but they were soon fired due to budget cuts. The two later met Lorne Michaels in late 1987 and they were given a three-week try-out in the Saturday Night Live writing staff. While on the staff, he won an Emmy Award for Outstanding Writing for a Variety, Music or Comedy Program. Daniels left the writing staff in 1990.
Daniels joined the writing staff of The Simpsons in 1993. He was hired in the fifth season following the departures of many of the original team of writers. His first day also coincided with O'Brien's last day on the series. When he initially joined the series, he believed the series had gone past the "glory years" and that he had "missed the boat." In the fifth season, Daniels penned "Homer and Apu," "Secrets of a Successful Marriage" and "The Devil and Homer Simpson" segment of "Treehouse of Horror IV." Daniels received an Emmy nomination in the "Outstanding Individual Achievement in Music and Lyrics" category for the song "Who Needs The Kwik-E-Mart?" from "Homer and Apu". For season six, he wrote "Homer Badman," "Lisa's Wedding," and the "Time and Punishment" segment from "Treehouse of Horror V." The latter episode became the third of the series to win a Primetime Emmy Award for Outstanding Animated Program. In the seventh season, Daniels wrote "Bart Sells His Soul," which was based on a childhood experience. His final credit for the series was for "22 Short Films About Springfield," which he served as supervising writer alongside show runner Josh Weinstein. They were given the responsibility of linking all the stories together.
Daniels left The Simpsons to work on King of the Hill alongside Mike Judge. Daniels rewrote the pilot script and created several important characters that did not appear in Judge's first draft (including Luanne and Cotton), as well as some characterization ideas (e.g., making Dale Gribble a conspiracy theorist). Daniels also took the writers to Texas to do some research with reporter notebooks, a process he would use for The Office and Parks and Recreation. Judge was ultimately so pleased with Daniels' contributions that he chose to credit him as a co-creator, rather than give him the "developer" credit usually reserved for individuals brought on to a pilot written by someone else. During the fifth and sixth seasons, Judge and Daniels became less involved with the show. They eventually focused on the show again, although Daniels steadily became more involved with other projects.
In 2005, Daniels adapted the popular BBC mockumentary series The Office for American audiences. The series premiered to mixed reviews, so the writers worked to make it more "optimistic" and make the lead character, Michael Scott, more likable. The second season was better received and it was named the second best TV series of 2006 by James Poniewozik, writing that "Producer Greg Daniels created not a copy but an interpretation that sends up distinctly American work conventions [...] with a tone that's more satiric and less mordant. [...] The new boss is different from the old boss, and that's fine by me." He gave the acceptance speech at the 58th Annual Primetime Emmy Awards when the American version of The Office won the award for Outstanding Comedy Series, and he received an award for Outstanding Writing for a Comedy Series at the 59th Annual Primetime Emmy Awards.
Following the success of The Office, Ben Silverman asked Daniels to create a spin-off for the series. After considering several ideas, Daniels and co-creator Michael Schur eventually decided that the series would not get a spin-off because Daniels and Schur "couldn't find the right fit." After Amy Poehler agreed to play the lead, they decided their new series would revolve around an optimistic bureaucrat in small-town government. The premise of Parks and Recreation was partly inspired by the portrayal of local politics on the HBO drama series The Wire, as well as the renewed interest in and optimism about politics stemming from the 2008 United States presidential election. The series initially received mixed reviews, much like The Office in the first season, but after a re-approach to its format and tone, the later seasons received critical acclaim. For four years, he split his time between The Office and Parks and Rec, before eventually returning as full-time showrunner for The Office for its ninth and final season.
In 2011, Daniels made a deal with NBC to produce several series for Universal Television. He also developed the British series Friday Night Dinner for American audiences. The remake was picked up for a pilot, which was written by Daniels and directed by Ken Kwapis, and featured Allison Janney and Tony Shalhoub as the mother and father. The pilot was eventually not picked up for series. He also teamed with Mindy Kaling and Alan Yang to work on two differing animated series for NBC and made a deal to executive produce a new pilot written by Office writer Owen Ellickson and starring Office cast member Craig Robinson.
Daniels met Susanne Dari Lieberstein while she was answering phones at Saturday Night Live for Lorne Michaels. They eventually married and had four children: Maya, Charlotte, Haley, and Owen. She is the sister to Paul Lieberstein, writer for King of the Hill and the replacement showrunner of The Office for Daniels. He is also the brother-in-law to Office writer Warren Lieberstein and Office cast member Angela Kinsey until her divorce in 2010.
Daniels' work has received mainly positive reception. Out of the six TV series that Daniels has worked on, four of them—Saturday Night Live, The Simpsons, King of the Hill and The Office—were named among Time reviewer James Poniewozik's All Time 100 TV Shows. His work on The Simpsons has received acclaim from critics and fans. Two of his episodes, "Bart Sells His Soul" and "22 Short Films About Springfield," were listed among the show's creative team's top five favorite episodes in 2003. Series creator Matt Groening and executive producer James L. Brooks have named his episodes among their favorites. Other staff members and several critics have praised his work. His other animated series and his first credit as a creator, King of the Hill, has received positive reviews as well. IGN named it the 27th best animated television series, and the site mainly complimented the series for its subtle character humor. The series currently ranks as the third-longest running animated television series, after The Simpsons and South Park.
His next television series, The Office, ranked as NBC's highest rated show for a majority of its run, according to the Nielsen ratings. The series has also been put on several top series lists by many publications including Time, BuddyTV, Metacritic, The Washington Post, and Paste. His writing credits for the series are often considered the best of the series. Despite its early acclaim, later seasons have received criticism for a dip in quality, notably after Daniels was less involved. Daniels' next series, Parks and Recreation, has been called "the smartest comedy on TV" by Entertainment Weekly.
Daniels has received several awards and nominations. He has been nominated for twenty Emmys and has won four. Those wins are for: Outstanding Writing for a Variety, Music or Comedy Program for his work on Saturday Night Live, Primetime Emmy Award for Outstanding Animated Program for the Simpsons episode, "Lisa's Wedding," Outstanding Comedy Series for The Office and Outstanding Writing for a Comedy Series for The Office: Gay Witch Hunt. Daniels was also awarded Austin Film Festival's Outstanding Television Writer Award in 2008.Saturday Night Live (1987–1990) – writer
Not Necessarily the News (1990) – writer
Seinfeld (1992) – writer
"The Parking Space" (co-written with Larry David) (1992)
The Simpsons (1993–1996) – co-executive producer, producer, co-producer and writer
"Treehouse of Horror IV" ("The Devil and Homer Simpson" segment co-written with Dan McGrath) (1993)
"Homer and Apu" (1994)
"Secrets of a Successful Marriage" (1994)
"Treehouse of Horror V" ("Time and Punishment" segment co-written with Dan McGrath) (1994)
"Homer Badman" (1994)
"Lisa's Wedding" (1995)
"Bart Sells His Soul" (1995)
"22 Short Films About Springfield" (supervising writer) (1996)
King of the Hill (1997–2009) – co-creator, executive producer and writer
"Pilot" with Mike Judge (1997)
"Hank's Unmentionable Problem" (co-writer with Mike Judge) (1997)
The Office (2005–2013) – developer, show runner, executive producer, director and writer
"Pilot" (co-writer) (2005)
"Basketball" (writer and director) (2005)
"The Dundies" (director) (2005)
"Halloween" (writer) (2005)
"The Client" (director) (2005)
"Booze Cruise" (writer) (2006)
"Valentine's Day" (director) (2006)
"Drug Testing" (director) (2006)
"Conflict Resolution" (writer) (2006)
"Gay Witch Hunt" (writer) (2006)
"The Coup" (director) (2006)
"Traveling Salesmen" (director) (2007)
"The Return" (director) (2007)
"Beach Games" with Jennifer Celotta (co-writer) (2007)
"Fun Run" (writer and director) (2007)
"Baby Shower" (director) (2008)
"Niagara" (co-writer with Mindy Kaling) (2009)
"Murder" (director) (2009)
"PDA" (director) (2011)
"Goodbye, Michael" (writer) (2011)
"New Guys" (writer and director) (2012)
"Finale" (writer) (2013)
Parks and Recreation (2009–2015) – co-creator, executive producer, director and writer
"Pilot" (co-written with Michael Schur; director) (2009)
"Hunting Trip" (director) (2009)
"Pie-Mary" (director) (2015)
The Mindy Project (2013) - director
"Mindy Lahiri is a Racist" (director) (2013)