In 1896, he created the tenor lead, Mike Murphy, in Charles Villiers Stanford's opera Shamus O'Brien, also playing the role on tour and in America.
After a series of concert engagements in London, O'Mara travelled again to America to create the tenor lead in Reginald De Koven's The Highwayman.
In 1909, O'Mara returned to Britain and joined the Thomas Beecham Company, singing tenor leads over the next few years, while also continuing to perform in concerts.
At eighteen he sailed for a year aboard an ocean liner travelling between Dundee and Calcutta before returning to his father's business, "totally cured" of the desire to live a life at sea.
In 1896, he created the tenor lead, Mike Murphy, in Charles Villiers Stanford's opera Shamus O'Brien, with Henry Wood conducting.
After a tour of Britain and Ireland in Shamus O'Brien, the Harris company brought the opera to America in 1897, where, with his new wife, the former Miss Power, O'Mara enjoyed great personal success.
O'Mara gave many private concerts at the beginning of the new century, but happily returned to opera as leading tenor with the Moody-Manners Opera Company in London from 1902 to 1908, performing in Maritana, Cavalleria, Faust, Lohengrin, Pagliacci, Il trovatore, Carmen, Charles Gounod's Roméo et Juliette, and the first English-language production of Puccini's Madame Butterfly (1907),[6] also performing extensively in Ireland with the company.
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.
[8] In 1909, O'Mara returned to Britain and joined the Thomas Beecham Company, singing in Carmen, Faust and Tales of Hoffmann, among others over the next few years, while also continuing to perform in concerts.
The Irish Times of Dublin wrote in February 1918: "Mr. O'Mara's Lohengrin is to my mind one of his best parts, it is not a hurricane of passion like 'Tannhäuser', it demands a purer vocalism, a quiet dignity, a calm and spiritual character, and yet, at the back of it all, an abundance of reserve power.