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". He was a leading tenor with the Moody-Manners Opera Company in London from 1902 to 1908, also performing extensively in Ireland with the company. O'Mara was granted the Freedom of the City of Limerick in 1908, the only time that a singer achieved this honour. In 1908, in Patrick Bidwell's musical "Peggy Machree" on Broadway in New York City. 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. In 1912, he founded O'Mara's Travelling Opera Company, in which he was the principal tenor until his farewell performance as Lohengrin in 1926. In all, O'Mara sang 67 tenor roles. In 1926, he was the first tenor to broadcast in Ireland.