[6] Cosgrove's first matchday involvement with the senior team came while he was still a second-year scholar, as part of his development process, when manager Malky Mackay named him as a substitute for the FA Cup third round visit to Bolton Wanderers on 3 January 2015.

[7] but after his winning goal in a Lancashire Challenge Trophy match, Chorley manager Matt Jansen said that Cosgrove had "pace to burn, he's big and strong and if he believes in himself he could do very well.

He spent the second half of the on loan at North Ferriby United,[18] made 14 National League appearances (3 starts) without scoring,[7] and was released by Wigan when his contract expired.

[7] He made an unexpected first start on New Year's Day in a loss to Mansfield Town, he was man of the match in a goalless draw with Championship club Sheffield Wednesday in the FA Cup,[22] his contract was extended to the end of the season, and on 13 January he scored his first goal to secure a 1–0 win against Crewe Alexandra.

[27] After playing just 11 minutes in the Scottish Cup over the next few weeks, he made his first Aberdeen start on 27 April, set up a goal for Anthony O'Connor in a 2–0 win against Hearts,[28] and helped them beat Celtic in the last match of the season to finish as runners-up.

[29] Aberdeen legend Willie Miller wrote that Cosgrove was well placed to fill the striker vacancy caused by Adam Rooney's departure, and might have the mentality to seize the opportunity, but his impression was that manager Derek McInnes felt he "still [had] a lot of developing to do".

[30] McInnes spoke of the importance to the team of his "size, his strength, his willingness to occupy defenders" after Cosgrove scored an "emphatic header" against West Bromwich Albion in pre-season.

[31] In the Europa League qualifier against Burnley, he won a penalty, converted by Gary Mackay-Steven to open the scoring in a 1–1 draw;[32] although they lost the second leg after extra time, he took confidence from performing well against top-class defenders.

[41] Strike partner Stevie May saw the team's improved creativity as a factor in Cosgrove's greater effectiveness,[42] while McInnes highlighted how a focus on "movement, anticipation and speed of thought"[43] helped him react more like a smaller striker than a pure target man.

[47] He set himself a 30-goal target, last achieved for Aberdeen by Joe Harper in 1978–79,[48] but a seven-match goal drought and a back injury left him on 23 and the team in fourth place when the season was curtailed because of the COVID-19 pandemic.

He then damaged a knee and was out for three months,[51] during which time he was one of eight Aberdeen players who were heavily fined by the club and received a suspended three-match ban from the Scottish Football Association after breaching COVID protocols by visiting a bar as a group.

[7] Incoming head coach Lee Bowyer, tasked with achieving Championship survival, selected Scott Hogan and Lukas Jutkiewicz as his strike pairing of choice.

[60] He joined League One club Shrewsbury Town on 11 August 2021 on loan for the season,[61] and made his debut three days later away to Morecambe, replacing Nathanael Ogbeta at half-time with his side 2–0 down.

[67] Cosgrove played twice for Birmingham in the 2023–24 EFL Cup and was a regular on the bench in Championship matches,[7] before he was released on 1 September to enable him to join League One club Barnsley on a two-year contract.