For the following 07–08 season, McCormick started as back-up to Larrieu, but got his chance as number 1 again when Larrieu was loaned out to Yeovil Town. After a 2–1 defeat to Sheffield Wednesday, McCormick lost his spot to the returning Larrieu, who played in a dozen games before falling ill to testicular cancer again, seeing McCormick become first choice once again. He received his first red card of his career in the 71st minute of a 1–0 defeat away to Scunthorpe United, for handling the ball outside his area. Defender Lee Hodges took over goalkeeping duties for the rest of the game, and emergency-loan signing Rab Douglas played the next game, before McCormick re-gained his place in the team, as Argyle went on to finish 10th in the Championship. A 1–0 defeat away to Wolverhampton Wanderers on 4 May 2008 would prove to be his final game for over four years. McCormick had played 157 games for Argyle, appearing as a substitute once.

On 7 June 2008, McCormick was arrested by patrol units of the Central Motorway Police Group on suspicion of causing death by dangerous driving. McCormick’s Range Rover collided with a Toyota Previa at 5.45am between junctions 15 and 16 of the southbound M6 motorway, near Keele Services in Staffordshire. The crash resulted in the death of Arron and Ben Peak, aged ten and eight, from the Partington area of Manchester. Their father, Philip, the driver of the Previa, was taken to the University Hospital of North Staffordshire with fractures to the neck, back, ribs and swelling of the lungs, and a 49-year-old man and his two sons, aged eight and ten, were treated for minor injuries.

On 2 July 2008, McCormick was suspended by Plymouth Argyle, and his contract was cancelled by mutual consent on 22 July. He pleaded guilty to charges of causing death by dangerous driving and driving with excess alcohol, and received a sentence of seven years and four months’ imprisonment and a four-year driving ban on 6 October. McCormick served time at both HM Prison Ranby and HM Prison Channings Wood before being released from HM Prison Leyhill on 6 June 2012.

In May 2012, with his release from prison pending, Swindon Town announced their intention to offer McCormick a trial period, but they finished the trial in August 2012 without offering him a contract.

McCormick signed with Conference South club Truro City on a non-contract basis in November 2012 and made his debut against Farnborough in the FA Trophy on 10 November. Although in administration, Truro were permitted to sign a goalkeeper when their only other keeper, Tim Sandercombe, was injured.

McCormick played 11 times for Truro before he re-entered league football for the first time in four and a half years by signing for Oxford United of League Two on 31 January 2013, on a contract until the end of the 2012–13 season. He played 15 matches for Oxford, but lost his first team place to Max Crocombe by mid-April and he was released at the end of the season.

In May 2013, it was reported that McCormick in talks to return to Plymouth Argyle, five years after his departure; on 9 May 2013 he re-signed for the club on a one-year contract. McCormick managed to establish himself as Argyle’s first choice goalkeeper ahead of Jake Cole until he fractured and dislocated a finger on his left hand in a 1–1 draw with Mansfield Town on 1 February 2014, which ruled him out for the rest of the season. Despite this setback, McCormick signed a new 2-year contract with the club at the end of the season.

He joined League Two side Swindon Town in July 2018 after a successful trial. He signed a one-year contract. He made his debut on 7 August 2018 in a 4–0 defeat to Chelsea U23s in the EFL Trophy. When first-choice keeper Lawrence Vigouroux received a call-up for the Chile national football team, McCormick deputised, and kept his place when Vigouroux returned from international duty, after only conceding four goals in his first seven starts. Vigouroux eventually regained his place from McCormick in October, until 23 March when McCormick started in a 4–0 win against Morecambe, and played every game until the end of the season. He finished the 18–19 season playing 21 games, with 17 of those appearances coming in the league.

McCormick started the 19–20 season as first-choice, starting all 14 games in all competitions until a 2–1 defeat to Bradford City on 5 October 2019. Loan keeper Steven Benda then took over goalkeeping duties, leaving McCormick to only play one more game for the rest of the season: a 1–0 EFL Trophy defeat to Bristol Rovers.

Having rejected the offer of a contract extension at Swindon, on 28 July 2020, McCormick joined Plymouth Argyle for a third time. “We feel Luke will provide good competition with Mike Cooper for the first-team position,” said manager Ryan Lowe.