Sheridan was born in Worthing, Sussex, England, the daughter of actress Sally Savalas (née Adams).
Sheridan began her career as a fashion model, appearing in the pages of Vogue and on the cover of Cosmopolitan, shot by Francesco Scavullo.
Sheridan made her acting debut in 1984 in the short-lived US primetime soap opera Paper Dolls, which co-starred Lloyd Bridges and Morgan Fairchild. However, her breakthrough came in 1986 when she joined the cast of the CBS primetime soap Knots Landing as Paige Matheson. She started in a recurring role but had become a series regular by the 1988-89 season. Sheridan remained with the series for seven seasons until its end in 1993, and for her performance in the role she won the 1990 Soap Opera Digest Award for Outstanding Lead Actress: Prime Time and the 1991 Soap Opera Digest Award for Outstanding Heroine: Prime Time. The same year, she was named one of People Magazine's "50 Most Beautiful People". In 1990, she was cast as Lucky Santangelo in the television adaptation of Jackie Collins' Lucky Chances. She also appeared in several made-for-TV films, and after Knots Landing ended in 1993, she appeared in the theatrical films Spy Hard and Beverly Hills Ninja. In 1998, she auditioned for the role of Grace Adler on Will & Grace, though the role ultimately went to Debra Messing. However, Sheridan did make a guest appearance on the show in 2003.
In 2004, Sheridan was cast as Edie Britt in the ABC comedy-drama series Desperate Housewives. On 15 November 2004, Sheridan (in character as Britt) appeared with NFL wide receiver Terrell Owens in an introductory skit to that evening's Monday Night Football episode. Some observers condemned the skit as sexually suggestive (see video), and ABC later apologized for airing it. On 14 March 2005, the Federal Communications Commission ruled that the skit did not violate decency standards, because it contained no outright nudity or foul language. Sheridan was nominated for a 2005 Golden Globe Award for Best Supporting Actress and was ranked #48 on Maxim's 2006 Hot 100 List. In February 2009, during the show's fifth season, Sheridan announced her departure from Desperate Housewives. Her exit episode aired in April 2009 when Edie Britt was killed off. Unlike the other main characters who had been killed off over the years on Desperate Housewives, Sheridan did not make an appearance in the show's final episode which aired in May 2012.
In 2010, Sheridan was cast in an untitled CBS comedy pilot as a mother who battles with her British ex-husband to get her teenaged daughter to stardom, but the show was not picked up. In September 2010, Sheridan starred in the Hallmark Channel film, Honeymoon for One, which was set in Ireland. The film premiered on the Hallmark Channel on 13 August 2011. In 2013, she starred and co-produced another Hallmark movie, called The Christmas Spirit. In an interview in November 2013, Sheridan announced that she was hoping to find a network for a half-hour comedy series that she is currently writing herself.
From 1979 to 1985, Sheridan dated singer and actor Leif Garrett. She met Garrett when he spotted her with his friend Danielle, whom he was picking up from the school where she and the friend attended, and Sheridan hopped in his car to go home. At aged 15, she moved into his family home with permission from his mother and her mother. After her career took off shortly afterwards, she left him and began dating other teen idols such as Scott Baio, Jimmy Van Patten, and Roger Wilson. Two decades later, Garrett credited Sheridan for helping him at the start of his career, and said of her, "She's a special person in my life."
Sheridan married actor Harry Hamlin on 7 September 1991. The pair had starred together in the 1990 TV movie Deceptions. Hamlin filed for divorce on 21 August 1992.
She began seeing Swedish personal trainer Nicklas Söderblom in 2004 and became engaged to him on New Year's Eve 2004; the pair called off the engagement in October 2005.
In 2005, Sheridan returned to ex-boyfriend Michael Bolton, whom she originally had dated for five years starting in 1992. Sheridan and Bolton announced their engagement in March 2006. In March 2008, Sheridan posed nude for a London Fog charity ad which also featured Bolton. Sheridan and Bolton broke off their engagement in August 2008. Sheridan married Aaron Phypers in December 2015 and filed for divorce on 15 July 2016, giving 19 June 2016 as the date of separation.
In April 2010, Sheridan filed a $20 million lawsuit against Desperate Housewives creator/producer Marc Cherry and ABC Television, alleging that she was assaulted by Cherry on the set of the show and was then fired when she reported the alleged abuse to the network. In her lawsuit, Sheridan claimed wrongful termination, assault and battery, gender violence, discrimination based on sex, sexual orientation and age, and intentional infliction of emotional distress. She also alleged that Cherry was abusive to other cast members and writers. ABC responded by stating that while they were unaware of this particular complaint, they had investigated similar claims made by Sheridan and reportedly found them to be without merit. The show's stars, Teri Hatcher, Felicity Huffman, Marcia Cross and Eva Longoria, pledged their support to help Cherry in his battle against Sheridan's allegations.
In May 2011, a judge granted permission for the case to continue to trial, but threw out Sheridan's claims of harassment. The case finally went to court on 27 February 2012. Cherry asserted that the alleged assault was in fact a tap to the head with his fingers, done in rehearsals when he was demonstrating to Sheridan how she should play a physical gag in a scene. He also stated that the decision to kill off her character was already approved in May 2008 (several months before the alleged hitting incident in September 2008) due, in part, to the need to reduce the show's budget. He also cited Sheridan's unprofessional on-set behavior (such as habitual lateness, not learning her lines, and feuding with her co-stars), and the fact that her character had simply "run its course" as other reasons for the decision. On 13 March 2012, the judge dismissed the battery charge against Cherry due to lack of evidence, and the lawsuit then focused solely on Sheridan's alleged wrongful termination by ABC. Closing arguments were heard on 14 March 2012 and the jury began their deliberations. By 19 March 2012, the twelve members of the jury had failed to reach a verdict and a mistrial was declared. A retrial was scheduled for September 2012, but this was dismissed in August when the Los Angeles Court of Appeal determined that Sheridan had not been wrongfully fired. The court rejected Sheridan's argument that ABC’s decision not to renew her option for another season was analogous to a violation of at-will employment. The court reasoned that unlike an at-will employee whose contract could remain in force indefinitely, Sheridan’s contract was for a set term that had expired and therefore ABC had not terminated her but simply chosen not to rehire her for another fixed-term contract. However, the court declared that Sheridan was free to file an amended lawsuit alleging that ABC retaliated against her for complaining about unsafe working conditions. A further appeal made by Sheridan to the California Supreme Court was rejected in November 2012, A new trial based solely on the retaliation claim was set for December 2013, but this too was dismissed in October 2013 by a judge who stated that Sheridan should have exhausted her claims through a labor commissioner before pursuing a trial. A further attempt by Sheridan to secure a new trial was refused on 16 January 2014, however the same judge reversed his decision on 29 January 2014 and granted Sheridan a new trial. In a further twist, this decision was later reversed in August 2014 by the Los Angeles Court of Appeal who found the judge's decision to grant Sheridan a new trial was in error.