O'Mara achieved a number of "firsts" for Ireland and Irish tenors: He was the first tenor in Ireland to sing Enzo in "La Gloconda" and in 1908 the first such Rodolfo in "La bohème". Later he was the first to sing Cavaradossi in Ireland and in the same season was in the Irish premiere of "Samson et Dalila." O'Mara's fame spread even further when he starred, in 1908, in Patrick Bidwell's musical "Peggy Machree" at The Broadway Theatre in New York City, earning uniformly enthusiastic reviews for his acting as well as his singing. In 1909, O'Mara returned to Britain and joined the Thomas Beecham Company, singing in "Carmen", "Faust" and "Tales of Hoffman", among others over the next few years, while also continuing to perform in concerts.