Forrest is stated by Anthony Wood to have been a relative of John Forest, the Franciscan friar.
He received his education at Christ Church, Oxford, and he was present at the discussions held at Oxford in 1530, when Henry VIII sought to procure the judgment of the university in the matter of his divorce; he appears to have attended the funeral of Queen Catherine of Aragon at Peterborough in 1536.
Forrestum," and "1581" occur in a volume (British Library Harley MS 1703) containing a poem which in a devout tone treats of the life of the Blessed Virgin and of the Immaculate Conception.
These manuscripts came into the hands of William Heather, founder of the musical praxis and professorship at Oxford, and are preserved in the archives there.
In 1548 he dedicated his version of the treatise De regimine Principum to the Duke of Somerset, and also in 1551 his paraphrase of some of the Psalms.