Tointon was born to parents Ken and Carol in Southend-on-Sea, Essex. She and her Actress sister Kara (born 1983) were brought up in Leigh-on-Sea and attended St Michael's School, Leigh, and St Hilda's School in Westcliff-on-Sea.

Tointon's first appearance on television was in the CBBC hit sitcom Kerching!, where she played Tamsin, the love interest of the main character Taj Lewis. Her next role was in the series Star 2003 where she played the character Billie. Following this, she played Celina Johnson in the British police drama series The Bill. She also portrayed Casey in the horror film The Children.

In 2006, she appeared in the television series Murder City, where she played Bethany Williams in the episode "Just Seventeen". She also appeared in Dream Team as Savannah Caskey. She then went on to appear in New Tricks, and had an uncredited part in the film Just My Luck as a concert goer, along with sister Kara. In early 2007, she appeared as Annabelle in Genie in the House, and also played Maxine Brogan in Doctors.

It was announced on 3 November 2007 that Tointon had quit Hollyoaks to try new things, and that she will have played the character of Katy Fox for a year. She said that her intention was always to stay just for a year.

She also starred in The Children, a horror film which co-starred Jeremy Sheffield; it was released in November 2008.

In April 2010, Tointon appeared in the Cornetto Enigma TV advertisement. She appeared as Simon's girlfriend Tara, in Series 3 of the Channel 4 sitcom The Inbetweeners. Filming in Spring 2010, she appeared from the second episode to the fourth.

Tointon moved in with The Inbetweeners co-star Joe Thomas in 2012, after they met earlier working on the show. The couple got engaged in 2017 and are currently living in London.

In September 2017 it was announced that she will be appearing in a new production of Strangers on a Train. The production is expected to tour from 5 January to 31 March 2018.