Her maternal grandfather, Antoin Ned McDevitt (1825–1917), would tell her his memories of the Great Famine, and the family were all opposed to the Anglo-Irish Treaty and the creation of the Irish Free State.
Due to the poverty in County Donegal, her brothers emigrated to the United States, and Harkin became a committed republican socialist.
She was introduced to Charlie Harkin in October 1932 at the Mansion House at a céilí raising money for the Republican Prisoners' Dependants' Fund.
Charlie was active in Clan na Gael, and introduced her to a circle of Dublin republican socialists, including George Gilmore, Cora Hughes, and Bobbie Walsh.
[3] Harkin became a supporter of left-wing republicanism in rejection of the militaristic and chauvinistic nationalism associated with Éamon de Valera, compounded by the implicit subjugation of women in the 1937 Irish constitution.
She was a member of the Republican Congress executive, taking part in protests and demonstrations which were cleared from the streets by Gardai with batons.
In 1937, she was a founding member of the New Theatre Group, which performed contemporary American and European leftist drama under the leadership of Thomas O'Brien.
In 1973, while establishing diplomatic relations with the USSR, the then Minister for Foreign Affairs Garret FitzGerald lauded the society's work in developing a relationship between the two countries.
She died at Ashbury Nursing Home, Kill Avenue, Blackrock, County Dublin on 7 June 2012, and is buried in Deans Grange Cemetery.