Franks worked for 14 years in theatre both in the UK and abroad. Her roles included the title role in Tess at The Kings Head Theatre in London for which was Time Out’s Critics Choice, and Sylv in Steven Berkoff’s 25th Anniversary production of East at the Vaudeville Theatre in London’s West End and on tour. Tanya then rose to prominence when her TV career began in 2000, after being cast in the Channel Five soap opera Family Affairs as Karen Ellis. Franks continued in the soap opera for three years, with storylines including a cancer scare, infertility, surrogacy, and a child custody battle, before leaving the series in 2003. In 2004, Franks was cast as DI Rowanne Morell in the long-running ITV1 police serial drama The Bill. Franks stayed with the serial for over a year, with her character investigating various murders of police officers and police corruption.
Franks appeared as a guest lead in an episode of the BBC1 medical serial-drama Holby City and in 2006, Franks appeared in an episode of the BBC1 drama series Doctors.
In 2006, Franks starred opposite Sharon Horgan and Rebekah Staton in the BBC Three comedy series Pulling. Franks was cast as Karen, a promiscuous, raunchy, aggressive primary school teacher, who drinks heavily and is not suited to her job, for which she was nominated at The British Comedy Awards in 2009. The sitcom ran for two series and a special feature episode, and gained a BAFTA nomination for best comedy series.
In July 2007, it was announced that Franks would play the role of Tanya Branning’s sister, Rainie Cross in the BBC One soap opera EastEnders for a week-long stint from 2 August 2007. Franks returned to EastEnders as Rainie in January 2008, and again in August 2010. She returned again in April 2011, before departing once more later that year. She made a surprise return to the show on 16 June 2014. EastEnders announced on 18 January 2018 that Franks would make a guest appearance the following day and return permanently later in the year. Tanya made her full time return on 24 April 2018.
Franks starred as Sandra Farrell in the BBC Two mocumentary The Cup. In 2009, Franks appeared in an episode of the E4 teen drama Skins. In 2010, she appeared in an episode of the BBC1 time-travelling drama Ashes to Ashes.
From September 2010 to August 2011, Franks starred as a series regular in the CBBC comedy serial Hotel Trubble. Franks also appears in Episode 7, Series 9 of New Tricks as literary agent Roxanne Guthrie. In 2013 she was a guest lead in an episode of Pramface as Fiona. Tanya plays Richard Burton’s wife, Sybil, in the 2012 made-for-television film Liz & Dick. In 2013 Tanya played Lucy Stevens, sister to DC Ellie Miller played by Olivia Colman, in the award winning series Broadchurch and continued her role throughout the second series. Franks continued to star in further theatre roles, including leading roles at the Royal National Theatre in Sing Yer Heart Out For The Lads by Roy Williams in 2004, The Black Album by Hanif Kureishi in 2009, and in the premier run of Really Old, Like Forty Five in 2010.
In 2013 she toured as Irene Adler in the new mystery Sherlock Holmes: The Best Kept Secret, and played the title role in Bertolt Brecht’s The Good Person of Sichuan at the Mercury Theatre in Colchester. Early 2015 she starred opposite her Sherlock Holmes’ co-star Jason Durr for a second time in the world premier of Contact.com at the Park Theatre in London, in which she was also reunited with EastEnders’ Charlie Brooks. Tanya was back on the boards in London in 2016 at the Menier Chocolate Factory in The Truth by hit playwright Florian Zeller, adapted by Oscar winner Christopher Hampton, and directed by the highly acclaimed director Lindsay Posner. Due to being a sell-out hit, it transferred to the West End’s Wyndham’s Theatre and the production was nominated for a Laurence Olivier Best New Comedy award.
Franks founded Stock-pot Productions in 1993, a theatre and film production company. Theatre credits included Scenes of Shaw at London’s Theatre Museum starring Les Dennis and the late great Paul Eddington; Deckchairs at London’s Kings Head Theatre in which Tanya also co-starred.
Co-productions included the national tour of You Don’t Kiss and All Fall Away which the Guardian named Pick of the Week with Tanya playing the lead role at the Latchmere Theatre (now Theatre 503). The company has made three short films, the last of which Franks wrote, produced, and starred in, entitled One Day. It was officially selected at several national and international film festivals and was Kodak best short film finalist. In addition to Franks, the film starred Tim McInnerny as well as Toby Stephens in a cameo role. In 2015 Tanya was in the new hit E4 comedy series Chewing Gum as Mandy, as well as filming in They Still Steal The Old Way with Ian Ogilvy, Chris Ellison, and Patrick Bergin, playing Governor Pryce, and the indie movie Moondogs. In 2016 she guest-starred in Vera, episode ‘The Moth Catcher’, and in episode five of Grantchester. Tanya played the antithesis Mum ‘Carol’ to Lesley Manville’s ‘Cathy’ in the BBC comedy hit series Mum, co-starring Peter Mullan and Lisa McGrillis.