[2][3] In 2016, the BBC included her in the list of 100 Women for "inspirational and influential women for 2016"[4] O'Sullivan has been a pro-choice believer since the early 1990s, when the X Case made the news, and had an abortion herself a few years later.

[5] As the spokesperson for the Abortion Rights Campaign, she has frequently written in national newspapers, and appeared on radio and TV about the abortion debate in Ireland.

[6] O'Sullivan is also a Bi-Visibility activist who has campaigned for Marriage Equality.

[7][8] O'Sullivan was in favour of the repeal of the Eighth Amendment and is working towards the goal of repealing the amendment and introducing legislation both in Ireland and Northern Ireland which ensures that women have the right to choose.

[9] On April 3, 2018 she registered as a third party with SIPO, the Irish government ethics watchdog.