He had been pragmatic towards the religious changes of the Reformation but probably remained most sympathetic to Catholicism.
His brother Geoffrey Glyn had left property and money in his will in 1557 towards the founding of a grammar school in Bangor, which William Glyn and Maurice Griffith, Bishop of Rochester were intended to execute. Both these men were to die the following year before the intention could be executed, but ultimately Friars School, Bangor was set up.