[2] A move into midfield led to Earls being convinced to return to St Munchin's,[2] and he won the Munster Schools Rugby Senior Cup with the college in 2006.

[5] During the 2007–08 season, Earls was part of the Munster squad that beat Toulouse in the 2008 Heineken Cup Final.

[6][7] In the 2008–09 season, Earls really made his mark in the Munster first team, scoring 10 tries, including a hat-trick in the Celtic League against Dragons in September 2008[8] and a brace in the Heineken Cup quarter-final against Ospreys in May 2009[9] Earls started against Northampton Saints in Munster's 31–27 round 1 2009–10 Heineken Cup defeat on 10 October 2009.

[18] Earls was also part of the Munster team that beat Leinster to win the 2011 Magners League Grand Final.

[43] Earls came off the bench against Saracens in round 5 of the 2014–15 European Rugby Champions Cup on 17 January 2015, winning his 100th cap for Munster.

[49] Earls started the opening pool game of the 2015–16 European Rugby Champions Cup against Benetton on 14 November 2015.

[52] On 22 October 2016, Earls was sent-off in Munster's 38–17 win against Glasgow Warriors in round 2 of the 2016–17 European Rugby Champions Cup.

[58] He won his 150th cap for Munster in the provinces 27–22 Champions Cup semi-final defeat at the hands of Racing 92 on 22 April 2018.

[59] Earls was named the 2018 Munster Rugby Player of the Year in April 2018, having previously been nominated for the same award in 2010.

[65] Earls scored two tries, the latter the match-winner, in Munster 17–13 win against Edinburgh in their 2018–19 European Rugby Champions Cup quarter-final on 30 March 2019.

[66] Earls signed a one-year contract extension with the IRFU in March 2021,[67] and scored two tries in Munster's 40–33 home defeat against Toulouse in the last 16 of the 2020–21 Champions Cup on 3 April 2021.

[70] Earls earned his 200th cap for Munster in their 22–22 draw away to South African the Sharks in round 18 of the 2022–23 United Rugby Championship on 22 April 2023, becoming the fourteenth player to do so for the province.

[87][88][89][90][91] Earls was selected in Ireland's squad for the 2011 Rugby World Cup warm-ups in August,[92] playing in both tests against France.

[95] He started on the wing against the United States in Ireland's first Pool C game, and again against Australia during their historic 15–6 victory over the Wallabies.

He returned to the left-wing for Ireland's final Pool C game against Italy and, on his birthday, scored a brace of tries in the 36-6 win.

[104][105][106][107] Earls played at inside centre for Ireland in the first test against New Zealand on 9 June 2012, as part of a new centre-combination with Brian O'Driscoll.

[124] He started in the first World Cup warm-up against Wales on 8 August 2015, scoring a try and earning the Man-of-the-Match award in the 35–21 win for Ireland.

[128] Earls started the second pool game against Romania on 27 September 2015, scoring two tries and earning the Man-of-the-Match award in Ireland's 44–10 win.

[143] However, his two-week suspension as a result of the red card he received against Glasgow Warriors meant that Earls missed Ireland's historic first ever victory against New Zealand in Soldier Field, Chicago on 5 November 2016.

[153] On 10 June 2017, in the one-off test against the United States, Earls scored two tries, made three assists and won the Man-of-the-Match award in Ireland's 55–19 win in the Red Bull Arena, New Jersey.

[156] Earls started every game for Ireland as they won a Grand Slam in the 2018 Six Nations Championship, scoring a try against Italy.

[173] During the World Cup itself, Earls started in Ireland's shock 19–12 defeat against hosts Japan,[174] the 35–0 win against Russia,[175] the 47–5 win against Samoa in their final pool game,[176] and the comprehensive 46–14 defeat against New Zealand in the quarter-finals, which brought an end to Ireland's 2019 World Cup.

[177] Retained by new head coach Andy Farrell in his squad for the 2020 Six Nations Championship, Earls featured off the bench in Ireland's 24–14 win against defending-champions Wales[178] and their 24–12 defeat against England,[179] before the tournament was suspended due to the COVID-19 pandemic.

[180] With the usual format of end-of-year international tests not possible due to the COVID-19 pandemic, Ireland instead participated in the Autumn Nations Cup.

[199] Earls missed Ireland's 2022 Autumn Nations Series due to a thigh injury[70] and also missed the 2023 Six Nations Championship due to a calf injury,[200] but returned for Ireland in their 33–17 win against Italy on 5 August in both nations' first 2023 Rugby World Cup warm-up match,[201] and earned his 100th cap for Ireland in their second warm-up match on 19 August, scoring one try in their 29–10 win against England having replaced James Lowe during the second-half.

[202] Earls was selected in Ireland's 33-man squad for the 2023 Rugby World Cup,[203] and started in their opening 82–8 win against Romania on 9 September.

[206] A week later, against Currie Cup outfit the Free State Cheetahs, he put in a far improved showing, scoring an impressive try which ultimately proved crucial to the result, with the Lions coming through to win 26–24.

On receiving the ball at the out half position and stepping past three rushing defenders, he touched down for the Lions' only try in a 13–13 draw.

[208] Earls also played against Western Province and Southern Kings in mid-week games,[209][210] but he did not win any full Lions caps on the tour.

[213] In the same month, during an appearance on The Late Late Show, Earls revealed he had been diagnosed with Bipolar II disorder eight years previously and opened up about his mental health struggles,[214][215] with then-Munster head coach Johann van Graan, amongst others, heaping praise upon Earls for his honesty and bravery.