|Date of birth||6 August 1977|
|Place of birth||Aalborg, Denmark|
|Height||1.91 m (6 ft 3 in)|
|Hartford Athletic (manager)|
|2010–2013||Sporting Kansas City||128||(0)|
|1999–2003||Denmark League XI||4||(0)|
|2013–2017||Oklahoma City Energy|
|* Senior club appearances and goals counted for the domestic league only|
Until June 2007, he played 398 games for Danish team AaB Fodbold. Playing every league match for AaB since 1997, Nielsen won the 1999 Danish Superliga championship with AaB. Nielsen has on occasion featured in the Danish national team setup as an unused substitute. He won the 1998 and 2004 Danish Goalkeeper of the Year award.
Nielsen began his career with Norwich City at the age of 12. He was discovered after Norwich City's youth team traveled to Aalborg to take part in a local youth tournament but their only goalkeeper, Ash Harrison, fell ill and Nielsen was recruited as a replacement. He played for Norwich City until the age of 15 when he was offered professional terms but his mother refused permission for him to move permanently to England. Following this he was signed by local amateur club B 52/Aalborg FC. He played youth football for AaB Fodbold, before signing for English club Millwall F.C. in 1994. He did not play for the club and moved back to Denmark, settling in at AaB in 1995. He made his senior debut in 1996, quickly becoming the starting goalkeeper in AaB. Nielsen was one of the cornerstones of AaB, culminating in the 1998–99 Danish Superliga championship.
Nielsen signed a contract with Leicester City on 4 June 2007. He joined via Martin Allen's agent, who claimed he was "another Peter Schmeichel". However, he was left in the reserve squad following the arrival of Hungarian goalkeeper Márton Fülöp. As a result, Nielsen revealed he planned to leave the club during the January transfer window, and was given the green light to do so on 14 November. He left the club on 22 January 2008 having his contract terminated by mutual consent without ever having played for the club. The next day he signed a 2½-year contract with Danish team Vejle Boldklub. After the 2009 season, Nielsen was "very close" to retiring Vejle Boldklub, was relegated from the Danish Superliga.
Major League Soccer
In February 2010, after having a conversation with and receiving a contract offer from Peter Vermes, Nielsen moved to Major League Soccer team Sporting Kansas City. After his first season, Nielsen stated that he would love to stay with the club another two or three years before considering retirement again.
As reported on 15 December 2010, Nielsen signed a 1-year contract extension to stay with the club through at least the 2011 MLS season. He was sent off for a handball outside the box on 9 June 2011, in Sporting Kansas City's inaugural game at their new stadium, Livestrong Sporting Park. On 28 November 2011, Nielsen signed a contract extension with Kansas City through the 2013 season. The contract also included an option for the 2014 season. Nielsen received the 2012 MLS Goalkeeper of the Year award. He broke the club record with 0.79 goals against average and helped the team finish first in their division. Nielsen retired following the 2013 season, which saw him win the MLS Cup. He played the MLS Cup with broken ribs.
During a session with the Denmark national under-21 football team in 1999, Nielsen and U-21 teammates Allan Kierstein Jepsen and Peter Degn went to the Munkebjerg casino in Vejle at night to gamble. They were subsequently excluded from all national team practices, a ban that lasted several years. This earned Nielsen the nickname Casino-Jimmy.
- As of 17 April 2019
|OKC Energy||20 December 2013||16 November 2017||136||54||38||44||39.71|
|Hartford Athletic||5 September 2018||13||2||2||9||15.38|
- Aalborg BK
- Sporting Kansas City
- Lamar Hunt U.S. Open Cup: 2012
- MLS Cup: 2013
- MLS Eastern Conference (playoff): 2013
- MLS Eastern Conference (regular season) (2): 2010, 2012
- MLS All-Star (2): 2010, 2012
- MLS Best XI: 2012 
- MLS Goalkeeper of the Year: 2012
- Sporting Kansas City Most Valuable Player (2): 2011, 2012 
- Danish Goalkeeper of the Year (2): 1998, 2004
- MLS Save of the Week (6): 2010 (Week 9, 13, 14, 16, 21, 22)
- MLS Save of the Week (4): 2011 (Week 19, 21, 25, 32)
- MLS Save of the Week (6): 2012 (Week 7, 13-15, 18, 19, 31, 32)
- "Flown From the Nest - Jimmy Nielsen".
- "Football Weekly presents: The Gambler - the Jimmy Nielsen story". the Guardian.
- "Milan works his magic". Leicester Mercury. 27 September 2007. Archived from the original on 22 November 2007. Retrieved 24 October 2013.
- Nielsen set for Foxes exit, Sky Sports 2007-09-28. Retrieved on 2007-09-29.
- Nielsen set to quit Foxes, Sky Sports 2007-11-14. Retrieved on 2007-11-15.
- "Nielsen Moves On". Leicester City F.C. 24 January 2008. Archived from the original on 15 April 2012. Retrieved 24 October 2013.
- "Nielsen: Vejle får en sulten spiller" (in Danish). Tipsbladet. 2008-01-23.
- "Nielsen surprising even himself in KC renaissance". MLSsoccer.com.
- "Sporting Notebook: KC's "busiest offseason"". Sporting Kansas City.
- "Recap: Sporting open stadium with controversial draw". MLSsoccer.com.
- "Nielsen signs extension". Sporting Kansas City.
- "MLS Cup champion Jimmy Nielsen announces retirement after 19-year professional career". Sporting Kansas City.
- Brisendine, Steve. "Sporting Kansas City's Jimmy Nielsen takes a gamble on a new tell-all autobiography | THE WORD". Major League Soccer. Retrieved 10 December 2013.
- "Jimmy Nielsen named head coach of Oklahoma City Energy FC". energyfc.com. OKC Energy FC. Archived from the original on 20 December 2013. Retrieved 10 February 2014.
- Edwards, Andy. "Oklahoma City's USL PRO franchise to build soccer stadium with sights on MLS future". mlssoccer.com. MLS. Retrieved 10 February 2014.
- Jimmy Nielsen coach profile at Soccerway. Retrieved 21 April 2019.
- "By The Numbers: The White Puma's historic career with SKC". Sporting Kansas City.
- Wiebe, Andrew. "Sporting KC's Nielsen voted Allstate Goalkeeper of the Yr". MLS Soccer. Retrieved 28 November 2012.
- "Sporting KC announces 2012 team awards". Sporting Kansas City.
- "Nielsen adds sixth SOTW honor". MLSsoccer.com.
- "2011 MLS Save of the Week". MLSsoccer.com.
- Jimmy Nielsen at Major League Soccer
- Danish national team profile (in Danish)
- Complete League statistics at danskfodbold.com (in Danish)
- Vejle Boldklub profile (in Danish)
- profile at the Wayback Machine (archived 2007-09-27) (in Danish)
- Ex-Canaries profile
- Jimmy Nielsen at Soccerbase
| Vejle captain
| Sporting Kansas City captain