After working as a secretary, Jonsson began her TV career on TV-am in 1989 where she worked as a weather forecaster. From 12 September 1989, she was also the weather forecaster for Swedish TV3, broadcasting from London. In 1992 she moved into mainstream presenting and played host to numerous shows including Gladiators, the Big Breakfast, The National Lottery - plus two major international broadcasts in 1998, the Eurovision Song Contest and Miss World. She also modelled for Playtex Lingerie during this period. She was a team captain on the BBC TV quiz show Shooting Stars.
In 1990 she married TV cameraman Johnny Turnbull, but a few years later had an affair with Gladiators cameraman Phil Piotrowsky. She got back together with Turnbull, and they had a son, Cameron; however they divorced in 1995. She later had a relationship with James Crossley, better known as Gladiator Hunter.
She spent many days on tabloid front pages in 1998, after it was revealed she was the victim of domestic abuse at the hands of her then boyfriend, footballer Stan Collymore. Jonsson later took out an injunction preventing Collymore from releasing a sex tape involving the two, apparently made while they were on holiday in Cyprus - the video was later destroyed by Collymore.
She presented Dog Eat Dog (reality game show) from 2001 - 2003, on BBC1. In 2002 Jonsson had a short-lived relationship with England national football team manager Sven-Göran Eriksson. The event caused a tabloid frenzy as Eriksson had a long-term girlfriend - Nancy Dell'Olio - at the time. He later spurned Jonsson for a reunion with Dell'Olio for the 2002 World Cup. There was some suspicion that the alleged relationship with Sven, and the subsequent publicity, may have been an attempt to revive her flagging career and boost sales of her soon to be released Autobiography.
In 2002, Jonsson presented TV makeover show Home On Their Own, a show where children made amends to their house (how they wanted the house to be) during the course of a weekend, while their parents went on holiday. Some of the home improvements included an Austin Powers room, doorbells for the children and a cinema living room.
After the media attention, she decided to return to Sweden. The Swedish television network TV3 offered her the role as hostess of the Miss Sweden beauty pageant. She declined the invitation.
In March 2003, Jonsson was a contestant on the BBC's Comic Relief does Fame Academy.
In 2005, she appeared with four other celebrities on Channel 4's daytime show Come Dine With Me
On 20 January 2007 she joined 10 other celebrities to take part in the ITV reality TV show Dancing On Ice, where she was partnered with Pavel Aubrecht. With previous experience at skating in her native Sweden, Jonsson and was expected to go far in the event but finished 9th after being beaten in the skate-off by Kay Burley.
Her latest project was the confessional TV show, Ulrika: Am I A Sex Addict?, broadcast on Channel 4 on 20 March 2007. The show charted Jonsson's personal journey to uncover the truth about sex addiction. She has recently appeared on BBC1's Would I Lie To You? (2007).
In December 2008 Jonsson admitted she had turned down a part in Doctor Who because she felt she didn't have the acting experience.