The 28-year-old was tipped for big things early in his career, appearing three times for England's U21 side alongside the likes of current Three Lions regulars Jordan Henderson and Danny Welbeck.
Incredibly, Sunday's game looks set to be McCarthy's first chance to play at Wembley, despite having visited the stadium four times.
The first outing came in the 2012 Championship play-off final, with the stopper watching from the bench as his Reading side were defeat by Swansea. The following year, McCarthy received his maiden international call-up, but once again didn't get off the bench as England drew with the Republic of Ireland.
Having been Southampton's No. 2 goalkeeper until recently, he was also on the sidelines for last season's League Cup final defeat to Manchester United, with Fraser Forster preferred, as he was for the game against Spurs at their temporary home earlier this season.
However, after being preferred to the former Celtic man for the game against Manchester United, McCarthy hasn't looked back, playing every minute of every game including three FA Cup ties.
The 'Saints' have not won in the league in eight games, but remain in the mix for the unlikliest of cup triumphs, something that would make McCarthy just the third English goalkeeper to win the FA Cup since the turn of the century, with only David James (Portsmouth 2008) and Joe Hart (Manchester City 2011) having done so.
Standing in their way are last season's finalists Chelsea, and Manchester United, who broke Southampton hearts in the EFL Cup last term.