He had first become important as the King's surveyor and architect at Windsor. Here the King had undertaken important and extensive works for the improvement and extension of the castle. Wykeham had a strong natural taste for architecture, and seems moreover to have been a wise and practical man of business. He became the King's chaplain, his principal secretary, and the keeper of the Privy Seal. In 1367 he was elevated to the see of Winchester, and appointed Lord Chancellor.
He was a most liberal man, and had the interests of the people sincerely at heart. To posterity he is chiefly known by his munificence in founding Winchester School, and New College at Oxford, two foundations which have greatly promoted the cause of learning. He seems in all cases to have used his power and his wealth for the public good. But John of Gaunt and his party hated him on account of his wealth and position; whilst in Wiclif's eyes he was not spiritual enough for a bishop. Wiclif thought that no ecclesiastic ought to hold office, or busy himself in secular affairs. He no doubt alludes to Wykeham when he says bitterly, "Benefices, instead of being bestowed on poor clerks, are heaped ... on one wise in building castles, or in worldly business."
It was against Wykeham that the petition of Parliament against giving office to ecclesiastics was chiefly directed. He was forced to resign the seals. The other ecclesiastics in office had to give up their posts, and laymen, creatures of John of Gaunt, were appointed to fill them. Sir Richard le Scrope was appointed Treasurer, and Sir Robert Thorpe Lord Chancellor. The same Parliament also petitioned the King about the unsatisfactory state of the navy, and granted a subsidy for putting it into a proper condition; but no great expedition was planned to reconquer the lost possessions in France. The war went on in a desultory way, and nothing particular was gained on either side. The Commons were growing tired of paying for it. They further showed their animosity to the clergy by decreeing that the tax which was to be levied to provide the subsidy voted for the King, was to be raised also from all those lands which had passed into the hands of the clergy before the twentieth year of Edward I.