In the 2005-06 season he won the Scottish Football Writers' "Young Player Of The Year" Award, after some impressive performances and scoring 13 goals. He played as no 7 for Kilmarnock in the Striker position, but can also play on the left of midfield. A resident of Stewarton, Naismith attended Lainshaw Primary School and Stewarton Academy, whilst his footballing education took place with local junior team Stewarton Annick. He then played several years in the Kilmarnock youth team before signing for the Kilmarnock senior team.
Naismith's performances led to a two-day trial with Arsenal in August 2006. In the same month, Kilmarnock rejected a seven-figure bid for the player from Southampton.
In January 2007 Naismith scored his first professional hat-trick, in a 3-0 CIS Cup victory over Falkirk. In April 2007, Naismith received the Scottish PFA Young Player of the Year award for his efforts in the 2006-07 season.
On 4 June 2007 it was reported that Rangers had made a bid of around £400,000 for the striker, with Kilmarnock officials incensed by what they thought a derisory offer.. On the July 26, it was widely reported that Naismith had handed in an official transfer request. His agent hit out at Kilmarnock for not allowing Naismith to join his "boyhood heroes", Rangers, and he claimed that the Ibrox club would be the only transfer he would consider, however reports surfaced on the BBC suggesting Kilmarnock were close to accepting a bid of around £2m from Rangers' Old Firm rivals Celtic. Shortly afterwards Naismith withdrew his transfer request.
Naismith was injured during Rangers Scottish Cup semi final against St Johnstone on 20 April 2008 and following surgery in May 2008, Naismith was ruled out for up to a year.
On 1 June 2007 Naismith was called up to the Scotland squad for the first time and made his debut as a late substitute in the 2-0 win over the Faroe Islands.
On August 21, 2007, Naismith captained the Scotland U-21 team and scored the 4th minute winner against the Czech Republic U-21s. He has won 10 U-21 caps and scored three goals to date.