[7] Hanrahan made his Heineken Cup debut on 21 October 2012, coming on as a replacement in Munster's second round fixture against Edinburgh at Thomond Park.
[16] He was named Man-of-the-Match in Munster's 16–10 win against Scarlets on 21 December 2013, scoring 11 points and setting up Ronan O'Mahony's match-winning try with a crucial cross-field kick in injury time.
On 7 January 2015, it was confirmed that Hanrahan would leave Munster at the end of the 2014-15 season to join English Premiership side Northampton Saints.
[31] Hanrahan made his debut for Northampton on 24 October 2015, coming off the bench to replace the injured George Pisi in Saints' 42–16 win against Newcastle Falcons.
He started for Northampton in their opening 2015–16 European Rugby Champions Cup pool game against Scarlets on 14 November 2015, scoring 5 points in his team's 15–11 win.
[33] He made his competitive return for Munster on 30 September 2017, coming off the bench against Cardiff Blues in Round 5 of the 2017–18 Pro14 and scoring two tries in the provinces 39–16 win.
[35] Hanrahan started at fly-half in Munster's 2018–19 Pro14 opening win against South African side Cheetahs on 1 September 2018, scoring one try and four conversions in the provinces 38–0 victory.
[37] Hanrahan scored 20 points, including one try, three conversions and three penalties, and earned the Man-of-the-Match award in Munster's 30–5 Champions Cup pool two win against French side Castres on 9 December 2018, having been a late call-up to the starting XV after Joey Carbery reported a tight hamstring before the game.
[41] Hanrahan won the 2019–20 Pro14 Golden Boot award for the best kicker in the competition, ending the regular season with a 90.91% success rate.
[42] In round two of the 2020–21 Champions Cup on 19 December 2020, Hanrahan scored 24 points off the kicking tee for Munster in their 39–31 away win against French side Clermont.
[44] Hanrahan's try in Munster's 38–27 win against Cardiff Blues in round 3 of the 2020–21 Pro14 on 26 October 2020 won the Try of the Season award with both Eir Sport[45] and Rugby Players Ireland.
[46] Hanrahan joined French Top 14 club Clermont on a one-year contract, with the option of a second year, ahead of the 2021–22 season.
[47] He made his competitive debut for the club in their opening fixture of the 2021–22 Top 14 season away to Lyon on 5 September 2021, starting at fly-half and scoring a try in Clermont's 28–19 defeat.