Llanrhychwyn takes its name from Saint Rhychwyn (sometimes recorded as Rhochwyn), son of Helig ap Glannog, the prince who lived at Llys Helig before it was inundated by the sea, and now the subject of myth and legend.

In about 1230 Llywelyn endowed another church for the local community living on the valley bottom in the commotal centre, on the site where St Mary's, Trefriw now stands.

Morris Jones also records in Welsh that this church was "built by Llywelyn for [his wife's] use, and for the use of the inhabitants, for their kindness towards him, and that he donated a number of farms from the parish of Llanrhychwyn, naming them as the parish of Tref Rhiw Las.

The ancient oak door has wooden hinges, and the bell, which dates from the 13th century, possibly came from Maenan Abbey.

A popular belief, based on a misinterpretation of a line of poetry in the Red Book of Hergest by 18th- and early 19th-century antiquarian scholars, is that Taliesin (c. 534–c.599), the 6th-century Welsh bard and the earliest poet of the Welsh language whose work has survived, was an inhabitant of the area, living on the shores of Llyn Geirionydd and buried there.

Robert Williams (Trebor Mai) (1830–77) was born near the parish church and grew up in the village.

John Roberts (1828–1904) was a native of neighbouring Trefriw, and he used that name in his job as a printer and bookseller.

In Eisteddfodau he would assume the bardic name of Gwilym Cowlyd, and frequently levelled criticism at the Gorsedd for being too Anglicised.

The lane through Llanrhychwyn continues from Trefriw or Llanrwst (via several gates) to Llyn Geirionydd, one of the most popular lakes in the area.