In 1710 he was sent to Italy with the financial assistance of St Patrick’s Cathedral, Dublin (awarded in 1709) in order "to improve himself in the art of music".
In 1720 he produced Scarlatti's opera Amor d'un'ombra e gelosia d'un'aura under the title Narciso at the Haymarket Theatre, to which he added two arias and two duets of his own.
The disappointment affected Roseingrave psychologically; his behaviour reportedly became irrational at times, and he neglected his duties.
In Ireland, he mainly seems to have spent his retirement, a remarkable exception being the first and only performance of his opera Phaedra and Hippolitus on 6 March 1753 in Dublin.
He died at Dún Laoghaire in 1766 and was buried in his family's grave in the churchyard of St Patrick's Cathedral, Dublin.
They are at times highly chromatic, reflecting the dissonant approach of English music such as Purcell's viol consort fantasies.
One factor which led to increased esteem for Roseingrave in the 20th century (though even now his music is seldom heard in concert, as opposed to being included on recordings) was the enthusiasm demonstrated for his output by Constant Lambert.