Maher was one of ten children born to Delia A. (née O'Malley) and Joseph Maher, a schoolteacher, in Westport, County Mayo, Irish Free State. He was educated by the Irish Christian Brothers and emigrated to Canada in 1956 where he worked for an oil company before becoming interested in theater. He worked for three years with the Canadian Players before making his New York stage debut in Brendan Behan's The Hostage.