Robat Arwyn has composed ten volumes of songs, a variety of individual choral pieces and nine shows, including Er Mwyn Yfory and Plas Du.
Over the years he has been commissioned by the National Eisteddfod, the Urdd, Radio Cymru and the Young Farmers Movement, as well as the London Welsh Male Voice Choir, Bois y Castell, Côr Seiriol and others.
Atgof o'r Sêr was the commission piece for the Denbighshire National Eisteddfod in 2001 which was written for Bryn Terfel, Fflur Wyn and Rhuthun and District Choir. During the Eryri National Eisteddfod in 2005 Er Hwylio'r Haul was performed by Bryn Terfel, Mari Wyn Williams and the Eisteddfod's Youth Choir.
Amongst his latest works are a programme of six songs, Yn dy gwmni di, composed for his old school, Ysgol Dyffryn Nantlle, Penygroes. The work was performed in December 2008 by pupils from the school with a special appearance by Bryn Terfel. Arwyn was also commissioned to compose a set of three songs, Heddiw, ddoe, yfory, for Côr Cardi-Gân and the work was performed during the summer of 2008.