While bishop, Weseham wrote an Instituta for his clergy, in order to teach them Christian doctrine and help them select sermon topics. One of the subjects he wanted his clergy to cover the basics tenets of the Christian faith. To do this, he listed all the doctrines in the Apostle's Creed, and covered possible sermon themes relating to each doctrine. He also gathered learned men around him, including the Franciscan Brother Vincent, John of Basingstoke, a Greek scholar, and Ralph de Sempringham, who became Chancellor of the University of Oxford.
Weseham resigned the see in November or December 1256 and died about 20 May 1257. He resigned due to paralysis. He was buried in Lichfield Cathedral.