Capon was born at Salcott, near Colchester in Essex in 1480; he was educated at Cambridge University, graduating B.A.
[1] In 1516 he became a Master of Jesus College, Cambridge and in 1526, aged 46, he was appointed Rector of St. Mary's Church in Southampton and subsequently also Rector of St. Mary's Church, South Stoneham.
[2] In 1546, aged 66, William resigned from his post at Jesus College and went to live in Southampton.
Capon believed that this was a severe blow to education, so in his will he provided £100 towards the "erection, maynetenance and fyndinge of a gramer scole" in Southampton.
It was not until 1553, three years after Capon's death in 1550, that this wish was fulfilled and King Edward VI School, Southampton was founded by Royal Charter.