A casket containing the body of a deceased construction worker, Rafeeq (Musthafa), is flown from Dubai to the Calicut International Airport in Kozhikode, then transported by ambulance to its destination. While en route, the ambulance is ambushed by criminals hired by Muhammed Unni (Siddique) to retrieve the 100 kilograms (220 lb) of gold that he and his co-smugglers have hidden in the casket. When they open the casket, they discover the gold is missing.
Around the same time, Jayanthi (Andrea Jeremiah) arrives in Kozhikode from Mumbai in search of her missing husband, Ramesh (Ashvin Mathew), an Indian Revenue Service officer who frequently disappeared from home for various reasons, but is now a suspect in the gold smuggling. Jayanthi arranged for a taxi to drive her to various locations in her quest to find Ramesh. The taxi driver Raju (Mohanlal) appears to have an interest of his own in the circumstances surrounding Ramesh's disappearance. At Jayanthi's bidding, Raju drives her to the home of her mother-in-law (KPAC Lalitha) where he cooks for them and interacts in such a way to earn their trust. Jayanthi then asks Raju to drive her to Kochi to the office of her friend, Chandrasekharan (Vijayaraghavan), assistant commissioner of police. Chandrasekharan promises Jayanthi he will investigate the disappearance of Ramesh. After leaving Chandrasekharan's office, Raju drives Jayanthi to see Chandrasekharan's wife, Advocate Rekha (Muthumany), who is also her friend. During their chat, Jayanthi receives a surprise phone call from Ramesh. He explains that he is in Kovalam for an official meeting but will return home the next day, and insists that Jayanthi return home as well. Chandrasekharan later informs Jayanthi that the phone number Ramesh called from was actually in Kochi, not Kovalam. It is also revealed that Sudheer, Ramesh's brother is involved in the smuggling operation.
Meanwhile, Unni, Babu, Shaji, Shenoy, and MLA meet atop an apartment building to discuss the circumstances surrounding the gold they smuggled into Kozhikode and lost to an ambush while in transit from the airport. They suspect Ramesh is involved since he disappeared right after the incident. They devise a plan to kidnap Jayanthi in order to force Ramesh to return the gold. An unsuspecting Raju and Jayanthi become the targets of their surprise attack in which Jayanthi is rendered unconscious. Raju draws his concealed handgun and foils the kidnapping by shooting at his assailants. He collects the unconscious Jayanthi and transports her to a safe place. When she awakens, she finds herself surrounded by strangers. She also discovers that Raju is not just a taxi driver rather he is part of an investigation to find Ramesh and the missing gold. Raju explains to her that Ramesh was involved in the smuggling, and has since become the target of the criminals. Jayanthi returns to Rekha's home for safety, and Chandrasekharan begins investigating Raju who, in a turn of events, has raised suspicion.
Raju and his team, now disguised as Sabarimala pilgrims, rent a van hoping to catch Jayan. Raja's teammate, Ameer Amanulla (Abu Salim), pretends to be an informer for Arif Bhai (Joy Mathew). He lures Jayan into a trap by telling him a gift from Arif is waiting for him in the van. Jayan is captured and interrogated by Raju who questions the 30,000 Dirham Jayan received from Arif in Dubai, as well as the circumstances surrounding the death of Rafeeq. Jayan reveals that Rafeeq was purposely pushed off a building to his death as part of Arif's master plan to transport the gold, thinking no one would suspect the gold was hidden in his casket. The trail leads Raju to the home of Ramesh's parents where Ramesh has been hiding under the protection of his mother, who is also aware of the smuggling. Raju takes Ramesh into custody along with others involved in the crime but he lets Ramesh go. It is eventually revealed that co-smuggler Shaji (Suresh Krishna), a young politician had deceived Unni and took the gold for himself.
After Raju and his team retrieve the gold, they are detained by local police. Raju identifies himself as a RAW agent and his team as intelligence officers from various agencies of India. He discloses his real name as Rajeev Sathyamoorthy. The police release them so they can complete their investigation and allows them to go back to Mumbai. Near the end of the film, it is revealed that Raju and his team are the actual smugglers.
In 2013, Ranjith announced plans to produce a film for Aashirvad Cinemas, starring Mohanlal and Manju Warrier, which was scheduled for a 2014 release coinciding with the annual Vishu festival held in Kerala, India. Production was slated to begin in December 2013. The announcement of Loham received considerable media attention as it was Manju Warrier's return to the screen after leaving the film industry to marry actor Dileep. The media coverage was further heightened when Prithviraj Sukumaran joined the cast. However, the film was shelved soon after its official announcement. Ranjith explained it was dropped because the film's story resembled that of another film in the same language released during its pre-production time. It was Prithviraj who noticed that the ending sequence of the planned script was similar to that of Thira (2013).
Later that year, the director planned another film with the same production company starring Mohanlal, which was titled G for Gold. Filming was scheduled to begin on 10 January 2014 in Kozhikode and Kasargode, but production did not begin on schedule due to Ranjith's dissatisfaction with the screenplay. He revised the screenplay and re-titled the film as Loham. Loham was announced in February 2015.
Loham is the fifth film directed by Ranjith in which Mohanlal was cast in the lead role. Ajmal Ameer and Andrea Jeremiah were confirmed during the pre-production period. Gauri Nanda received boxing lessons to help her prepare for her role. Niranjana Anoop, a daughter of one of Ranjith's family friends, made her acting debut in the film as Mythri, a badly behaved youngster. Loham is the second collaboration between Ameer and Mohanlal, following Madampi (2008). Ajmal's character's looks were modelled after popular young politicians in the country, who are often spotted in the white kurta-jacket outfit. In March 2015, it was confirmed that Aju Varghese would play a guest role. Also Deepak Parambol who came to see Mohanlal in the filming location ended up in a guest role. In April, Srinda Ashab, Manikuttan and Parvathi Menon were also signed for guest appearances in a musical performance. The Hindu wedding song was shot in Kozhikode. Several media outlets reported Pearle Maaney was to perform an item number in the film but the report was determined to be incorrect after a selfie of Maaney dressed in a wedding outfit was leaked online. She appeared in a cameo role. Maaney's scenes were filmed in three days. Salim grew a beard and shaved his head for his role. He said, "My getup in the movie is similar to that of Dwayne Johnson".
Kunjunni S. Kumar, son of cinematographer S. Kumar, was hired as Loham's cinematographer. Kunjunni had first worked with Ranjith as an associate director during the production of Indian Rupee (2011) while his father worked behind the camera. Earlier, he was supposed to debut as a cinematographer on Ranjith's Leela in 2012, but the project was shelved ten days before production. In an interview with the Deccan Chronicle, Kunjunni said that after the script narration, Ranjith told him to avoid gimmicks in framing and shots in order to make it more realistic. Mythili, who was cast by Ranjith in her debut film, acted in and served as an assistant director for the film which was her debut behind the camera. She also sang a duet song in the film's soundtrack. Sreevalsan J. Menon was selected by Ranjith to compose the film's original music score. Renji Panicker suggested Menon to Ranjith during the film's pre-production stage. C. Rajamani composed the film score.
Principal photography began on 8 March 2015, at the Calicut International Airport in Kozhikode. M. D. Sasidharan, managing director of Gold Coin Motion Pictures, performed the switch-on, and K. R. Pramod, chief manager of Mathrubhumi, made the first clap. The film was shot in various locations including Kozhikode, Kochi, Delhi and Dubai. Production moved to Kochi after the shoot in Calicut. Willingdon Island and Fort Kochi were some of the shooting locations on the Kochi schedule. Filming wrapped in May 2015. Loham's production budget was estimated to be ₹7 crore (US$1.1 million).
On 18 March 2015, the first image capture from the film was released, featuring Andrea, Ranjith and Mohanlal on location in Calicut. The first-look poster featuring Mohanlal was released on 29 June 2015. More detailed posters were released during the first week of August. The first poster showed an ensemble cast with Mohanlal in the centre; their facial expressions indicative of the film's thriller genre. Other posters showed Mohanlal wearing army-style camouflage pants.
The first teaser of the film was 44 seconds long and was released on 12 August 2015. It received positive reviews in various media outlets with regard to Mohanlal's acting, and for the film's plot as a thriller. The teaser received over 200,000 views within 24 hours on YouTube, and over 400,000 views within three days. An official trailer 1.37 minutes long was released on 18 August 2015.
The film's music was composed by Sreevalsan J. Menon, and lyrics were written by Rafeeq Ahammed, Manoj Kuroor and Rajeev Nair. The first song, "Kanaka Mayilanchi", sung by Mythili, was released by Mathrubhumi Music on 13 August 2015. Mythili also sang a duet with Shahabaz Aman. The Times of India called it "a melody that remind [sic] listeners of the golden era of Malayalam cinema". The audio CD comprising three songs was released on 17 August during a function held at Kochi.
Loham was initially scheduled to be released in July 2015 during Ramadan, but it had to be postponed until 20 August because of delays in post-production. The film was then scheduled to open in India on 20 August 2015 as a festival release during the Onam season.
The film was distributed to 250 theatres across India, resulting in approximately 1000 screenings daily. On 20 August 2015, the film was released on 141 screens in Kerala, and to other theaters in India on 21 August 2015. The film's debut in the Middle East took place on 27 August 2015. It also opened in theaters in the UAE and UK on 28 August 2015. Rights for television broadcast was sold as a joint venture to Asianet and Kairali TV for ₹6 crore and ₹1 crore respectively. The film was released on DVD in India by Central Home Entertainment on 2 December 2015.
The film grossed ₹3.5 crore (US$550,000) on its opening day in India, with ₹2.20 crore (US$340,000) from Kerala box office receipts alone. Loham created a new opening day record in Malayalam that surpassed the previous record set by Casanovva in 2012. It collected ₹5.84 crore (US$910,000) in its first weekend (4 days) from the state. The national gross was ₹13 crore (US$2.0 million) within 22 days of the film's initial release, with ₹11 crore (US$1.7 million) from Kerala. Special screenings were arranged by some of the major releasing centres of Kerala. By the end of the first weekend, distribution of the film was increased to include more cities. The film collected ₹12.2 crore (US$1.9 million) from Kerala in its final run, generating ₹15 crore (US$2.3 million) in box office revenue worldwide.
Loham received mixed reviews from critics. Rejath R.G of Kerala Kaumudi said, "Renjith has beautifully conceived the film", and praised the technical aspects with special mention to Kunjunni's camera work and the three "beautiful" songs composed by Sreevalsan. He summarised it as "a watchable good film that could have been much better if the director paid a little more attention to the screenplay. The problem is that it loses steam here and there particularly in the post-interval sequences". Deccan Chronicle rated the film 2.5 out of 5 and said, "Any of [Mohanlal's] fans, who are exposed to thrillers of Hollywood and Bollywood like Ocean's 11 and Special 26 will lose the thrill soon. There is nothing commendable about the script or cinematography or music", but he praised Mohanlal's action sequences and car chasing scenes, Siddique and his companion's performances, and Mythili and Musthafa's "heart touching" moments. He called the message of the film "socially relevant" and "effective". Akhila Menon of Filmibeat also gave the film 2.5 out of 5 stars. He praised the performances of Mohanlal and Siddique, but was less enthusiastic about the script, observing that "Ranjith's craft as a filmmaker is visible throughout the movie. But what Loham lacks is his brilliance as a writer".
Pramod Thomas of The New Indian Express commented, "Mollywood has been in an experimental mode of late. Unfortunately, movies like Loham are many laps behind. . . . When Megalomaniac directors decide to live in the shadow of their past glory, films like Loham happen". Veeyen of Nowrunning.com gave the film 2 out of 5 stars and wrote "Loham has none of the shine or shimmer that was expected of it. At best it looks like an antique bronze piece that has taken some fine patina all over it", but he praised Mohanlal and Siddique's performances. Parech C. Palicha of Rediff.com commented, "Loham lacks lustre, and is not original at all". Sify praised the performance of Mohanlal and the humour of Siddique and Soubin Saheer but criticized the script, saying, "Loham is about a topical subject, but it is far from engaging". Raj Vikram of Metromatinee said that technically the film is slick with well shot sequences. "Mohanlal is the lifeblood of the movie, and he pulls off an easy role by his standards with characteristic panache . . . Loham is not among the best works of director Renjith but is far better than some of his forgettable duds."