After winning the FA Cup with Wigan in 2013 he moved to Everton, suffering from various injuries including a broken leg in 2018 which ruled him out for over a year.

Born and raised in Scotland, McCarthy elected to represent the Republic of Ireland at international level and made his competitive debut for their senior team on 26 March 2011 in a UEFA Euro 2012 qualifier against Macedonia.

[4] A former student of St Margaret Mary's Secondary School in Castlemilk,[6] he grew up supporting Celtic[7] and tried out for their youth teams, but was turned down due to the large number of players the club had already taken on.

[17] He was part of the Wigan Athletic team that overcame Manchester City in the 2013 FA Cup Final; afterwards he hailed manager Roberto Martínez as "a tactical genius".

[18] On 2 September 2013, McCarthy rejoined former Wigan manager Roberto Martínez at Everton, signing a long term deal worth £13m to become the club's second most expensive player in their history;[19] due to a clause in his Wigan contract, his former club Hamilton received a sell-on fee from the Everton transfer, which they used to invest in the youth system through which the player had emerged.

[20] He forged a partnership with Gareth Barry which was a key factor[21] in Everton amassing 72 points during the campaign, a club record in the Premier League.

[26] McCarthy eventually missed the rest of season due to a hamstring injury he had sustained whilst on international duty in March 2017;[27] Everton manager Ronald Koeman expressed his displeasure at Republic of Ireland manager Martin O'Neill selecting a half-fit McCarthy repeatedly, which had aggravated existing hamstring issues.

[29] McCarthy was ruled out for the rest of the 2017–18 season, and only made one further senior appearance for Everton, coming off the bench for the last 15 minutes of a home league fixture against Manchester United in April 2019, at which point his team were already 4–0 ahead.

[35] Despite multiple attempts to persuade McCarthy to switch his allegiance to the country of his birth, he reaffirmed his decision to play for the Republic of Ireland.

McCarthy made an instant impression, creating opportunities for the lone striker, as well as making many intelligent runs in behind the Turkish defence.

[48] This led to media speculation that McCarthy may switch his allegiance to Scotland, as his appearance in the friendly against Brazil did not tie him to Ireland under the present rules.

[50] The question of McCarthy's international allegiance was finally resolved in March 2011 after he accepted a call-up for Ireland's Euro 2012 qualification match against Macedonia, in which he came off the bench replacing Robbie Keane to earn his first competitive cap, rendering him ineligible to play for Scotland.

[52] On 7 May 2012, Giovanni Trapattoni confirmed that McCarthy had asked to be withdrawn from consideration for the Irish UEFA Euro 2012 squad following his father's diagnosis with cancer.