[10] The following season saw Marler play a crucial part in helping Harlequins claim their first ever League title by starting in the 2011–12 Premiership final victory over Leicester Tigers.

[13] In January 2016 it was announced that Marler had signed a new contract to stay at the club[14] and later that year he started for the Harlequins side that were defeated by Montpellier in the final of the EPCR Challenge Cup.

[15] On 26 June 2021 Marler won his second league title starting for the Harlequins side that defeated Exeter Chiefs 40-38 in the highest scoring Premiership final ever.

[25] Marler was selected for the 2012 summer tour of South Africa[26] and on 9 June 2012 made his senior debut starting in the opening test defeat to the Springboks.

[7] Coach Stuart Lancaster included Marler in his squad for the 2015 Rugby World Cup[30] and he started for the hosts in the pool stage as they failed to reach the knockout phase.

[31] New head coach Eddie Jones included Marler in his squad for the 2016 Six Nations Championship[32] and he came off the bench in the concluding game of the tournament as England defeated France to achieve their first grand slam in over a decade.

[34] He also started in the last round of the tournament defeat away to Ireland which ensured England failed to complete consecutive grand slams and also brought an end to a record equalling eighteen successive Test victories.

[38] Marler came off the bench for the semi-final victory over New Zealand and was a second half replacement for Mako Vunipola in the final as England were defeated by South Africa to finish runners up.

His comments were widely criticised, including by New Zealand coach Scott Robertson, with academic Karaitiana Taiuru saying that Marler "lacked cultural appreciation.

"[44][45] Marler later apologised for his "poorly articulated" words, saying that he "meant no malice in asking for it to be binned, just want to see the restrictions lifted to allow for a response without sanction.

[54] In December 2022, Marler received a 6 week ban (four of them suspended) for conduct prejudicial to the game involving insulting language used in an incident with Bristol Bears flanker Jake Heenan.

This was the subject of a 2021 Sky Sports documentary Big Boys Don't Cry, which was aired to coincide with Mental Health Awareness Week.