For a period in the late 1980s he was the bassist in Dublin rock band The Foremen, with whom he performed on the RTÉ TV show Jo Maxi in 1989.

His second book, Sinn Féin and the Politics of Left Republicanism was published by Pluto Press in 2009 and the launch was held in Pearse Street Public Library on 16 February 2009.

In 2013, Ó Broin was co-opted by Sinn Féin onto South Dublin County Council to represent Clondalkin local electoral area, after sitting councillor Matthew McDonagh resigned his seat.

[15] In May 2019, the election of Frances Fitzgerald TD as a Member of the European Parliament created a vacancy in the Dublin Mid-West constituency.

At the resulting by-election in November 2019, Ó Broin managed the campaign of the Sinn Féin candidate Mark Ward.

[21][22][23] Housing proved one of the key issues in the 2020 Irish general election and factored into Sinn Féin's significant gains in the voting.