Marsha Thomason

Thomason was born in Moston, Manchester to a Jamaican-born mother who arrived in England at age 10 and a father of English, Irish and Scottish heritage. Thomason attended Holy Trinity Church of England Primary School in Blackley and the (now defunct) North Manchester High School for Girls in Moston, and completed her A Levels at Oldham Sixth Form College. She graduated with a Bachelor of Arts (BA) in English from Manchester Metropolitan University. At age 13, Thomason joined Oldham Theatre Workshop, where she participated in youth theatre productions.

Thomason first came to prominence on British television playing Sally in the fifth series of the BBC One police procedural Pie in the Sky in 1997. This was followed by roles in 1998 as Sharon "Shazza" Pearce in Playing the Field, also on BBC One, and Jacqui Richard in the ITV series Where the Heart Is. Thomas had her first notable film roles in Black Knight (2001), Long Time Dead (2002) as Lucy and Pure (2002) as Vicki with Keira Knightley. In 2003, Thomas starred in Disney's The Haunted Mansion with Eddie Murphy, appeared in the first series of the BBC Three drama Burn It as Tina, and began starring in the NBC series Las Vegas as Nessa Holt, a role she would play for two seasons. On 21 October 2004, Thomason was a guest on the radio show Loveline. Thomason led the 2006 film Caffeine. In 2007, Thomason joined the recurring cast of the ABC science fiction series Lost as Naomi Dorrit. Being a friend of Dominic Monaghan (who played Charlie Pace on the series), she was a huge fan of the show and excited to be cast. In January 2008, she appeared in the BBC One drama Messiah V: The Rapture. In August 2008, Thomason was cast as a series regular in the CW comedy-drama Easy Money as Julia Miller. In late 2009, she appeared in the medical soap opera General Hospital. She also had a recurring role in the ABC Family teen gymnastics drama Make It or Break It. After appearing in the pilot episode for the USA Network series White Collar as agent Diana Berrigan, she returned for the first-season finale. Thomason was promoted to main for the second season, a role she would play until 2014. Thomason returned to British television in 2015, starring as Katy Carmichael opposite Christopher Eccleston in first series of the ITV crime drama Safe House. Thomason had a recurring role in seasons 9 to 11 of the CBS series NCIS: Los Angeles (2017–2020) as Nicole DeChamps. From 2020 to 2023, Thomason had a main role as fictional Labour Party MP Francine Bridge in the Sky One political thriller COBRA. In 2022, she joined the cast of the ITV crime drama The Bay for its third series as DS Jenn Townsend, taking over as lead from Morven Christie.

As of 2004, Thomason was based between London and Los Angeles. On 5 April 2009, Thomason married lighting technician Craig Sykes in Malibu, California. Their daughter was born in June 2013. Thomason became an American citizen in 2012.