In 1974, at age 20, Grant studied law at University of Sheffield, though he had no intention of entering the legal profession and, during his student days, worked backstage in a theatre. After graduating, he worked in commercial television.

Grant joined Granada Television, part of the UK's ITV Network, in Manchester as a presentation Director. There he was involved with shows including Brideshead Revisited, The Jewel in the Crown, Prime Suspect, and Cracker. Grant was involved in the transmission of more than 40,000 hours of programming for Granada, writing thousands of commercials and news stories. He worked at Granada from 1977 to 1995 and ended his career there with two years as a trade union shop steward.

After being made redundant from his job due to corporate restructuring, Grant decided to start writing novels, stating they are "the purest form of entertainment." In 1997, his first novel, Killing Floor, was published, and he moved to the United States in the summer of 1998.

In 2007, Grant collaborated with 14 other Writers to create the 17-part serial thriller The Chopin Manuscript, narrated by Alfred Molina. This was broadcast weekly on Audible.com between 25 September 2007 and 13 November 2007.

On 30 June 2008, it was announced that Grant would be taking up a Visiting Professorship at the University of Sheffield from November 2008. In 2009, Grant funded 52 Jack Reacher scholarships for students at the university.

Grant was elected President of the Mystery Writers of America in 2009.

In January 2012, Grant donated £10,000 (about US$16,000 at the time) towards a new vehicle for Brecon Mountain Rescue Team in Wales. His brother is a senior member of the team. The team's former control vehicle was written off after a collision in 2011.

In 2013, the Daily Mail quoted him saying that he writes while intoxicated ("high") by cannabis and that he has smoked the recreational drug five nights a week for 44 years. However, in a phone interview in November 2013, he clarified his comments to the Irish Examiner, saying he's never written while high. "Yeah, that's true," Child told The Post-Standard. "I mean, people say to me, 'There was that story in the newspaper,' and I say, 'No, that's The Daily Mail.' In Britain, that's not a newspaper, you know, that's a scandal sheet where they make stuff up. It's not very reliable. And certainly I don't deny smoking the occasional joint, but I don't work when I'm stoned because you don't get much done that way."

Grant has said that he chose the name Reacher for the central character in his novels because he himself is tall and when they were grocery shopping his wife Jane remarked: "'Hey, if this writing thing doesn't pan out, you could always be a reacher in a supermarket.' ... 'I thought, Reacher — good name.'" Some books in the Reacher series are written in first person, while others are written in the third person. Grant has characterised the books as revenge stories – "Somebody does a very bad thing, and Reacher takes revenge" – driven by his anger at the downsizing at Granada. Although English, he deliberately chose to write American-style thrillers.

In 2016, his eighteenth novel, Never Go Back, was adapted into Jack Reacher: Never Go Back, with Tom Cruise reprising the role. The movie was directed by Edward Zwick, and the screenplay was written by Richard Wenk, Zwick, and Marshall Herskovitz. In the film, the final scene is set in New Orleans, which was not a location in the book. The author approved this addition to help the New Orleans economy. In the film, Grant made a cameo appearance as a TSA agent. In the bonus footage on the Blu-ray disc, the author explained that in both movies his cameo appearance involves passing judgment on the character of Jack Reacher, and speculated that he will repeat these type of appearances in Future Jack Reacher movies.