Originally from St Mary's in the VMFL, Stevens was recruited in the 1997 AFL Draft to the Port Adelaide Football Club using pick 25. He was an under-16 All-Australian who was well suited to half back and ruck-roving. As he matured, he became a very prominent outside midfielder. In 1998, he was runner-up to Byron Pickett for the NAB rising star award. He also won awarded the inaugural AFL Players AssociationBest First-Year Player award. He managed to play every game in 1999 coming off half forward and the wing; he finished fourth in the club's best and fairest. In 2000, he continued to develop into a match-winner and finished second in the club's best and fairest after he missed five games due to suspension. Stevens played a total of 127 games for Port Adelaide, including back-to-back pre-season premierships in 2001 and 2002.
Carlton
At the end of the 2003 season, Stevens expressed a desire to return to his native Melbourne and wished to be traded to Collingwood. Port Adelaide was unable to obtain what it considered appropriate trade consideration, and, as a result, Stevens quit the club and entered the pre-season draft. He was subsequently drafted by Carlton with the second selection in that draft. Stevens was named vice-captain of the club in 2007, a position he held until his retirement. After Round 3, on advice from specialists, Stevens had surgery to heal a prolapsed disc in his neck, ending his season; he had sustained a neck injury in a front-on collision with Melbourne's David Neitz in late 2006 but had continued to play and train. The injury was a major blow to Carlton, as Stevens had been in fantastic form through the pre-season and early rounds. On 23 August 2007, it was announced that Stevens had signed with the Blues until the end of 2010. By his standards, Stevens had a poor season in 2009, struggling to make a strong impact in many games, and attracting criticism for deficiencies in his defensive game. During the midpoint of the 2007 season, Stevens was dropped to the VFL for a few games. At the conclusion of the season, it was revealed that Stevens had sustained another, more serious, recurrence of his neck injury from 2007, most likely caused by a collision with captain Chris Judd in Round 22. Facing the risk of permanent spinal damage if he played on, Stevens officially announced his retirement on 29 October 2009, with one year remaining on his contract. Stevens played a total of 104 games for Carlton and 127 for Port Adelaide.
Post-football career
Following his retirement from AFL, Stevens focused on expanding his business, NJS Signature Landscapes, in Melbourne. Additionally, he took on the senior coaching role of the NSW/ACT Rams for the AFL Under-18 Championships for 2010 and 2011; he had served as an assistant midfield coach for the team since 2006 while still playing for Carlton. In August 2011, Stevens made a return to the field, playing games for Montmorency in the Northern Football League, where he is still playing games in 2012. In November 2011, Stevens was appointed as senior coach at the Gippsland Power in the TAC Cup for the 2012 season. At the end of the 2013 season, Stevens joined South AustralianNational Football League club Glenelg as coach. Prior to Stevens' appointment the Tigers won just once in their last 15 games, finishing bottom in 2013.
Conviction
Stevens only served one season of his coaching contract and was sacked in January 2015, after he was found guilty of assault and threats to bash his ex-partner. In March 2015, Stevens was sentenced to eight months jail but appealed. He was again found guilty in July 2016, sentenced to six months jail, and fined $3,000.
