Inter-county Fenton was a member of the Dublin team that won an
All-Ireland Under-21 Football Championship in 2014. In 2015 Fenton made his senior debut, starting a national league game against Monaghan where he quickly scored a goal in a strong win. He won the
National Football League and the
Leinster Senior Football Championship with Dublin, starting both games in midfield. Fenton was named as the
Man of the Match in the
2015 All-Ireland Final, as Dublin defeated
Kerry on a 0-12 to 0-9 scoreline. Fenton won the
League title with Dublin in 2016 against Kerry in the final, scoring a point in the game. He was a key performer in Dublin retaining the Sam Maguire cup in 2016 which Dublin won after defeating Mayo by a single point after a
replay. He won his second All Star award in as many seasons and named on the shortlist for Footballer of the Year, which was ultimately won by Mayo's
Lee Keegan. In 2017 Fenton was part of the Dublin team defeated in the
National League final by Kerry, losing on a scoreline of 0-20 to 1-16. Despite this, he was crucial in Dublin retaining their Leinster title while beating a record held since the 70's by winning 7 championships in a row. Dublin retained their All Ireland title defeating Mayo in the
final again by a single point after
Dean Rock kicked a match winning free kick late in injury time. Fenton also scored a point to help Dublin over the line on a scoreline of 1-17 to 1-16. Fenton continued his success with Dublin in 2018, winning the National Football League, the Leinster and All-Ireland Championships. He was awarded an All Star and named the Footballer of the Year for his performances. On 14 September 2019, Fenton was a key player in Dublin's conquerage of Kerry to win the elusive five Sam Maguires in a row, which had never been done by any team before, though some teams came close with the four-in-a-row, including Kerry (twice). During Dublin's five-in-a-row, Fenton spent more time on the field of play than any other Dublin player, starting 35 of the 37 matches in the championship. Fenton played every minute of Dublin's historic six All Ireland's in a row campaign. On 18 November 2024, Fenton announced his retirement form inter-county football. ==Reception==