He fell out of favour with Villa manager Steve Bruce and was loaned to Nottingham Forest, Melbourne City, Central Coast Mariners and Motherwell before being released in 2019.

[4] He made his first appearance on 1 May 2004 against future club Motherwell at the age of 17, coming on in place of Mikel Arteta in the 61st minute of a 4–0 win at Ibrox.

[5] Fifteen days later, McCormack scored his first goal for the club in the final match of the 2003–04 season against Dunfermline Athletic at East End Park.

[6] On 23 November 2005, he made his European debut away to FC Porto in the UEFA Champions League group stage, replacing Francis Jeffers with 14 minutes remaining.

[7] McCormack's opportunities were limited in a Rangers side when Dado Pršo and Nacho Novo returned from injury and the club signed Kris Boyd from Kilmarnock in January 2006.

[9][10] McCormack made his Well debut on 30 July as the team began the SPL season with a 2–1 home loss to Rangers, in which he assisted their goal by Phil O'Donnell.

[14] In 2007–08, McCormack became a fixture in the Motherwell first team, where he found himself better suited to playing in a 4–3–3 formation, receiving the October 2007 Young Player of the Month award.

[16] In January 2008, McCormack was linked with a move to Premier League sides Wigan Athletic, even coming as close as having a contract ready to be signed with the club,[17] and Middlesbrough but no deal was agreed and he eventually signed for Championship side Cardiff City on 28 June on a free transfer, although the clubs would later agree on a compensation fee of £120,000.

[19] McCormack made his league debut on the opening day of the season in a 2–1 victory over Southampton and went on to score his first competitive goal for Cardiff in a 1–1 draw against Doncaster the following week.

[20] Amidst interest from Premier League clubs, on 8 August he was involved in three goals of a 4–0 win over Scunthorpe United in the first match at the Cardiff City Stadium.

[27] With two goals in a 3–3 draw against Brighton & Hove Albion on 23 September 2011, including an injury-time equaliser,[28] McCormack became the first Leeds player in over 50 years to score in six consecutive league games.

[41] Later in the month he entered negotiations for a new contract,[42] ending the uncertainty about the player's future after three separate bids by Middlesbrough in the region of £1.8 million.

With rumours of interest also from Sunderland on deadline day, McCormack released a statement via Sky Sports News that he pledged his future to Leeds and also his support of manager Brian McDermott, who was sacked only 30 minutes later.

[47] The next day, McCormack scored a hat-trick in a 5–1 victory against local rivals Huddersfield Town, taking his tally to 22 goals for the season.

[54] On 5 June, Leeds owner Massimo Cellino said he had rejected a substantial offer for McCormack from Newcastle United,[55] which that club denied.

[60][61] He made his debut on 9 August as Fulham began the season with a 2–1 loss at Ipswich, after which manager Felix Magath criticised his fitness level.

[62] Fifteen days later he scored his first goal for his new team, the only one in a League Cup second round victory at West London rivals Brentford.

[75] On 21 January 2017, Villa manager Steve Bruce revealed that McCormack had been dropped from the first team squad for "continually missing training", adding that "he is nowhere near fit enough to play and be involved".

[82] He made his debut in the season opener on 6 October, starting as his team defeated Brisbane Roar 2–0 at the Melbourne Rectangular Stadium.

[87] On 20 September 2018, McCormack signed a one-year loan deal with A-League club Central Coast Mariners FC.

[93] After making four appearances for Motherwell, McCormack returned to Aston Villa in March for treatment of a calf injury that had kept him from playing for a month.

[99] In February 2024, as part of a publicity stunt, alongside Charlie Mulgrew and Wes Hoolahan, McCormack signed for Central Midlands League North side Doncaster City.

[106] On 24 August, after scoring 4 goals in his first 5 games for Leeds during the 2013–14 season, McCormack's form earned him a recall to Gordon Strachan's Scotland squad for World Cup qualifiers against Belgium and Macedonia.

[107] On 27 October 2009, McCormack was arrested in Cardiff Bay on a drink-driving charge after crashing his Range Rover into metal railings in the early hours of the morning.

[109] In July 2013 McCormack was handed a £200 fine, ordered to pay £883.25 in costs and a £20 victim surcharge at a hearing at Leeds Magistrates' Court, for the offense of flytipping.