James has appeared in more than 20 films, including Les Misérables (1998), Snatch (2000), 24 Hour Party People (2002), Sahara (2005), and Outlaw (2007).
He starred in the 2010 film Tic and appeared in the action film Colombiana (2011) and the sci-fi film Lockout (2012).

On television, James appeared in the short-lived Channel 4 prison drama Buried (2003), the BBC terrorism drama The State Within (2006), the BBC spy drama Spooks (2002–2011), and he starred as Robert Hawkins in the CBS post-apocalyptic drama series Jericho (2006).
James appeared in a Channel 4 television drama Fallout (2008), playing the role of a detective alongside another detective solving a teen-related murder.
He also appeared in an episode of Lie to Me, as well as the 2009 AMC/ITV miniseries The Prisoner, of which he said, "It wasn’t necessarily the easiest gig I’ve ever been on, but it was always acting."
He appeared in HBO's comedy series Hung as a pimp.

James appeared in episodes of the 2010 TV series Human Target as the assassin Baptiste.
In 2012, he received critical acclaim for his appearance as DCI Tony Gates in BBC Two's Line of Duty, created by Jed Mercurio.

In 2010, he guest-starred as Morgan Jones in the pilot episode of the AMC series The Walking Dead, titled "Days Gone Bye".
In 2013, he reprised his role as Morgan Jones in an episode of the third season of The Walking Dead titled "Clear."
On 12 October 2014, James made his return to the show in a post-credit scene at the end of the fifth-season premiere and appeared again in a single scene at the end of the mid-season finale on 30 November 2014.
He returned for the fifth-season finale and played a significant role in the episode.
Despite his few appearances on the show, James has received significant recognition for his portrayal of Morgan from critics and fans, including being stopped by a policeman who wanted to talk to him about the show.
He returned as a main cast member in the show's sixth season until the eighth season.
As of 15 April 2018, James appears as Morgan in the fourth season of Fear the Walking Dead as a series regular.

On 29 March 2015, James' character was featured throughout the fifth-season finale.
The actor's post-show appearance on the Talking Dead—in which he did not speak with an American accent—caused the hashtag #morganisbritish to trend on Twitter.

James stars as Dr. Boyle on the medical drama Critical, also created by Mercurio, which debuted on Sky 1 in February 2015.
He spent nearly a year away from his home in Los Angeles to film the series.
Each episode takes place in "real time," with the medical staff having to save a life in an hour.
James spent a week shadowing doctors at a London hospital to prepare for the role.

James said his favorite television show of all time is the 1980s police drama Hill Street Blues, telling the Daily Express, "It’s the one that spawned every other show.
It’s the Muhammad Ali or Pelé of television shows."

James wrote the autobiographical TV film, Storm Damage in 2000, which was nominated for a British Academy Television Award for Best Drama Series.
Storm Damage depicts a teacher who tries to go back to the foster home he left and help the teenagers there, as James did.
He also wrote the play The Sons of Charlie Paora, which opened at London's Royal Court Theatre in 2004.

James has also portrayed the Destiny and Destiny 2 character Lord Shaxx who is the host of the in-game PVP (Player Versus Player) "The Crucible" in which he voices over matches and also has an in game vendor to purchase items, and bounties.
In an interview with GameSpot, Lennie stated his favorite line in the game, was in fact a line straight out of Shakespeare's Romeo and Juliet.
The line in question is in game as "But soft!
What light through yonder window breaks?
It is the east, and I--I am the Crucible."
James has appeared in more than 20 films, including Les Misérables (1998), Snatch (2000), 24 Hour Party People (2002), Sahara (2005), and Outlaw (2007). He starred in the 2010 film Tic and appeared in the action film Colombiana (2011) and the sci-fi film Lockout (2012).
On television, James appeared in the short-lived Channel 4 prison drama Buried (2003), the BBC terrorism drama The State Within (2006), the BBC spy drama Spooks (2002–2011), and he starred as Robert Hawkins in the CBS post-apocalyptic drama series Jericho (2006). James appeared in a Channel 4 television drama Fallout (2008), playing the role of a detective alongside another detective solving a teen-related murder. He also appeared in an episode of Lie to Me, as well as the 2009 AMC/ITV miniseries The Prisoner, of which he said, "It wasn’t necessarily the easiest gig I’ve ever been on, but it was always acting." He appeared in HBO's comedy series Hung as a pimp.
James appeared in episodes of the 2010 TV series Human Target as the assassin Baptiste. In 2012, he received critical acclaim for his appearance as DCI Tony Gates in BBC Two's Line of Duty, created by Jed Mercurio.
In 2010, he guest-starred as Morgan Jones in the pilot episode of the AMC series The Walking Dead, titled "Days Gone Bye". In 2013, he reprised his role as Morgan Jones in an episode of the third season of The Walking Dead titled "Clear." On 12 October 2014, James made his return to the show in a post-credit scene at the end of the fifth-season premiere and appeared again in a single scene at the end of the mid-season finale on 30 November 2014. He returned for the fifth-season finale and played a significant role in the episode. Despite his few appearances on the show, James has received significant recognition for his portrayal of Morgan from critics and fans, including being stopped by a policeman who wanted to talk to him about the show. He returned as a main cast member in the show's sixth season until the eighth season. As of 15 April 2018, James appears as Morgan in the fourth season of Fear the Walking Dead as a series regular.
On 29 March 2015, James' character was featured throughout the fifth-season finale. The actor's post-show appearance on the Talking Dead—in which he did not speak with an American accent—caused the hashtag #morganisbritish to trend on Twitter.
James stars as Dr. Boyle on the medical drama Critical, also created by Mercurio, which debuted on Sky 1 in February 2015. He spent nearly a year away from his home in Los Angeles to film the series. Each episode takes place in "real time," with the medical staff having to save a life in an hour. James spent a week shadowing doctors at a London hospital to prepare for the role.
James said his favorite television show of all time is the 1980s police drama Hill Street Blues, telling the Daily Express, "It’s the one that spawned every other show. It’s the Muhammad Ali or Pelé of television shows."
James wrote the autobiographical TV film, Storm Damage in 2000, which was nominated for a British Academy Television Award for Best Drama Series. Storm Damage depicts a teacher who tries to go back to the foster home he left and help the teenagers there, as James did. He also wrote the play The Sons of Charlie Paora, which opened at London's Royal Court Theatre in 2004.
James has also portrayed the Destiny and Destiny 2 character Lord Shaxx who is the host of the in-game PVP (Player Versus Player) "The Crucible" in which he voices over matches and also has an in game vendor to purchase items, and bounties. In an interview with GameSpot, Lennie stated his favorite line in the game, was in fact a line straight out of Shakespeare's Romeo and Juliet. The line in question is in game as "But soft! What light through yonder window breaks? It is the east, and I--I am the Crucible."
Lennie James