Finnish Under 21 international goalkeeper Jussi Jaaskelainen came to Norwich on trial from Finnish side VPS Vassa in October 1997. With City's Third choice keeper Robert Green out until after Christmas with injury, Mike Walker wanted extra cover for the No.1 shirt. Jussi played for the Reserves in their 1-0 victory over Luton Town on October 27th. He returned to Finland to await Walker's verdict.

Whilst Walker deliberated, Premiership side Bolton Wanderers stole City's thunder and signed Jussi for £100,000. He made his debut on Saturday 8th August 1998 in Bolton's 2-2 draw with Crystal Palace. He has been Bolton's first choice keeper during the 1998/99 season as injuries have plagued the other keepers in their squad. Despite a heroic performance in Bolton's FA Cup semi-final clash with Aston Villa that finished 0-0 on 2nd March 2000, Jussi could not stop Villa's penalty takers. After his Bolton teammates failed to convert their efforts, Jussi had to stop Dion Dublin or the Trotters would be out of the cup. Unfortunately for Bolton, the England international striker converted his chance to send Villa to the cup final

In July 2000, Jussi signed an extension to his contract until 2004. His impressive contribution to Bolton's fine start to their 2001/02 Premiership campaign led to speculation that Middlesbrough were preparing a £4million bid. He is also likely to add to his 7 international caps for the Finns.

When Peter Schmeichal announced his retirement in April 2003, speculation began almost immediately that Jussi would be signed by Man City as his replacement. In October 2004, Jussi's form in helping Bolton to the upper echelons of the Premiership saw him linked with Manchester United and Middlesbrough. However Jaaskelainen told the club's website. "It's just speculation. I don't care about it. I still have two years left,"

According to the News of the World on 24th April 2005, Arsenal are said to be closely monitoing Jussi's contract negotiations with Bolton but nothing materialised. With Bolton swooping for Oman international and highly rated keeer Ali al Habsi in January 2006, it appears that Jussi's stay at Bolton may come to an end. Middlesbrough are said to be watching the situation, according to the News of the World (8th January 2006). In May 2006, he was linked with a £2.5million switch to Portsmouth. Staying with Bolton, Jussi was linked in May 2007 with a move to Sunderland for £2m and to Newcastle following Sam Allardyce's departure from Bolton to take charge at St James' Park.

At the beginning of October 2007, a number of media sources reported that Jussi's agent having said that he will not sign a new contract at Bolton because he wants to team up again with Sam Allardyce - now at Newcastle. On 14th April 2008 the Daily Mirror claimed that "Aston Villa boss Martin O'Neill is set to swoop for Bolton goalkeeper Jussi Jaaskelainen, who is out of contract in the summer. O'Neill is unwilling to pay Liverpool £10m for on-loan Scott Carson, so he has turned his attention to the 32-year-old Finn instead"

On 23rd November 2008, Jaaskelainen was named by the News of the World as a target for new Tottenham manager Harry Redknapp following the erratic form of Spurs' Brazilian keeper Heurelho Gomes.

Bolton were relegated from the Premiership on 13th May 2012 although Jussi made only 10 appearances that season (bringing his total for Bolton to 519). Out of contract, he was linked with a switch to West Ham, newly promoted to the Premiership. This became reality at the beginning of July 2012.

He was released by the Hammers at the end of the 2014/15 season having made 61 appearances. He trialled with Bradford City in July 2015.

On 11th August 2015, he signed a one year contract with Wigan. He was in goal when they secured promotion to the Championship on 30th April 2016 with a 4-0 win over Blackpool. He was released by Wigan on 17th May 2017 following their relegation to League One on 29th April 2017. He had made 48 appearances for Wigan.

On 1st September 2017, he joined Indian Super League side ATK, making his debut three months later but leaving the club in January 2018 (although some reports had him staying on in a coaching role).

He then joined Wrexham as a goalkeeping coach but left on 7th June 2019 to return to Finland.