Sligo Rovers at The Showgrounds on 28 May 2013. Despite a number of injury problems, Mountney featured in 23 matches in 2013 and found the net on two occasions, helping Dundalk secure second place in the League. He penned new deals committing himself to the club for both the 2014 and 2015 seasons. Playing more games than anyone else in 2015, he added a League and FAI Cup Double to the League and League Cup medals won in 2014. In October 2015, Mountney signed a new contract for the 2016 campaign. Mountney remained a key member of the side for Dundalk's three-in-a-row League title success in 2016 and, despite some injury setbacks, won more honours as Dundalk won both the League title and the FAI Cup in 2018 - the club completing its second Double in four seasons. Mountney signed a two-year contract extension at the end of the 2018 season. On 21 December, it was announced that Mountney had departed Dundalk after nine seasons at the club. St Patrick's Athletic On 7 January 2021, it was announced that Mountney had signed for Dublin club St Patrick's Athletic, managed by his former Dundalk captain Stephen O'Donnell. After signing for the club, O'Donnell asked Mountney to tell his new teammates how they were regarded by a title-winning team (Mountney's Dundalk team) as a motivational tactic. He made his debut for the club in the opening game of the season, playing at right back in a 1–1 draw away to Shamrock Rovers in a Dublin derby on 19 March 2021. He scored his first goal for the Saints on 30 July 2021 with a deflected free kick from 30 yards away to Shamrock Rovers in what was his 350th career appearance. Mountney suffered a cruciate ligament injury in a 4–1 win away to his old club Dundalk on 8 August 2021, an injury that put him out for the rest of the season. On 28 November 2021 his club won the 2021 FAI Cup Final, beating rivals Bohemians 4–3 on penalties following a 1–1 draw after extra time in front of a record FAI Cup Final crowd of 37,126 at the Aviva Stadium with Mountney missing out through injury but receiving a medal following his appearance in the first round of the tournament. Return to Dundalk On 24 December 2021, it was announced that Mountney had followed head coach Stephen O'Donnell back