In October 2015, McCarthy signed a loan deal until February with Wycombe Wanderers,[6][7] with the deal later extended until the end of the season.[8] At the end of the season, he was voted Supporters' Player of the Year.[9]
Walsall (loan)
On 28 June 2016, McCarthy was sent out on loan to Walsall for the first half of the season.[10][11] He scored his first goal for Walsall in a 1–0 win over Bolton Wanderers on 17 September 2016.[12]
On 1 January 2017, McCarthy's loan to Walsall was extended until the end of the 2016–17 season.[13]
At the end of the season, he was crowned the Fans Player of the Season after playing every minute of every game in the 2016–17 season for the Saddlers.[14]
Barnsley
On 13 June 2017, he joined Barnsley for an undisclosed fee on a three-year deal.[15]
Wycombe Wanderers
On 9 August 2018, McCarthy returned to Wycombe Wanderers where he had previously been on loan, signing for an undisclosed fee on a three-year deal.[16] McCarthy won the Supporters' Player of the Year Award for the 2018–19 season.[17]
Millwall
On 30 July 2019, he was transferred to Millwall for an undisclosed fee on a three-year deal.[18]
Wycombe Wanderers (second loan)
On 18 January 2020, McCarthy once again rejoined Wycombe Wanderers on loan until the end of the 2019–20 season.[19]
Wycombe Wanderers (second permanent spell)
On 25 August 2020, McCarthy rejoined Wycombe Wanderers for a fourth time, signing a three-year contract for an undisclosed fee.[20]