Porter attended Portobello High School in Edinburgh. She studied for a BTEC HND in media production at West Herts College. After making an unsuccessful bid to join the presentation team of the BBC children's show Blue Peter, she has presented family-friendly television programmes, or ones aimed at children. They include The Movie Chart Show, Top of the Pops, and Live & Kicking, work for CITV, and programmes such as The Big Breakfast and Gail Porter's Big 90s for VH1.
In the late 1990s she began to pose for magazines such as FHM. A nude photograph of Porter was projected on the Houses of Parliament in 1999. FHM and the guerrilla marketing company, Cunning Communications, and projectionist-artist Malcolm Litson and Jason Bridges, accompanied it with a message to vote for her in the FHM Sexiest Women Poll.
In her autobiography, Porter says she did not know about the stunt until it was reported the following day.
In 2001, Porter took part in the reality television show Celebrity Blind Man's Bluff. and on Lily Savage's Blankety Blank. In 2003, she was on Channel 4's The Games, although injury curtailed her participation.
In 2004 to 2006 she presented three series of Dead Famous and in 2009 presented episodes of The Gadget Show, temporarily replacing Suzi Perry. In 2008 to 2011, Porter was a regular panelist on Channel 5's The Wright Stuff.
In early 2009, Porter's mother died of lung cancer, aged 60.
In 2010, she was a guest team captain on What Do Kids Know? with Rufus Hound, Joe Swash and Sara Cox on Watch. In August 2010, she began the Two Way Street campaign for solicitors Russell Jones & Walker, an initiative to develop the relationship between HGV drivers and cyclists, keeping them safer. In October 2010, Porter hosted a documentary on Current TV, Gail Porter on Prostitution which investigated prostitution laws.
In 2014, Porter said she would be guest editor of Fashion Plus magazine.
She appeared at London Fashion Week in September 2014 and wrote of her experiences for the magazine.
On 27 August 2015 she entered the Celebrity Big Brother house representing the UK. On 15 September, she was the fourth housemate to be evicted after spending 20 days in the house.
In 2017 she became the brand ambassador for the insolvency practitioner Creditfix, meeting with the public and speaking openly about her struggles with debt in several corporate videos.
In 2005 Porter developed alopecia totalis, losing her hair. She decided not to wear a hat or wig in order to raise awareness of the condition, and to remain true to herself. She became ambassador for the Little Princess Trust, a charity which provides wigs to children with hair loss. On Richard & Judy on 15 February 2006 she showed her hair, eyebrows and eyelashes were beginning to grow back. On 12 April 2006 she said "It is possible that I'm going to get my hair back."
By May 2010 hair had grown on three-quarters of her scalp, and she was beginning to colour and style her hair. By the end of the year, her hair had started falling out again.
Porter's alopecia totalis was the subject of the BBC ONE Life series documentary Gail Porter Laid Bare on 31 May 2006. Her autobiography, Laid Bare: My Story of Love, Fame and Survival, was published in September 2007.
She is a vice-president of The Children's Trust, a UK charity for children with brain injury.
Porter tried stand-up comedy and appeared at the Comedy Store on 23 November 2009 in the Laughing Point event to help the youth homelessness charity, Centrepoint.
Porter married Toploader guitarist Dan Hipgrave in August 2001 and gave birth to their daughter Honey on 3 September 2002. She said in February 2005 that they had separated eight months earlier.
Before they met, Porter was in a relationship with Keith Flint, vocalist from The Prodigy.
Porter has been diagnosed with bipolar disorder, and says she has insomnia.
On 8 September 2011 Porter told BBC Radio 5 Live's Phil Williams that she had been detained under the Mental Health Act of 2007, for 17 days of treatment against her will. She stated the signature on the documents to have her sectioned was that of her boyfriend, after texting to him to say she felt suicidal. She said she had been "very frail, so who knows". She said she felt no benefit from the stay. She praised the staff but said the resources and facilities were under-funded.