Cynddelw began his career as court poet to Madog ap Maredudd, Prince of Powys.
At Madog's death in 1160, Cynddelw wrote the following elegy: While Madog lived there was no man Dared ravage his fair borders Yet nought of all he held Esteemed he his save by God's might… If my noble lord were alive Gwynedd would not now be encamped in the heart of Edeyrnion.
Cynddelw composed poems for a number of the later rulers of Powys, now divided into two parts, such as Owain Cyfeiliog and Gwenwynwyn.
Cynddelw was known in his time for opposing superstition, and the monks of Strata Marcella in Powys sent "a deputation to him with a requisition that he should renounce his errors, and make satisfaction to the Church, threatening, in case of non-compliance, that he should be excommunicated and deprived of Christian burial.
Which, translated, reads, "Since no covenant would be produced against me, which the God of purity knows, it would have been more just of the monks to receive than to reject me.