Molyneux was the son of Sir Richard Molyneux, 1st Baronet of Sefton and his wife Frances, the daughter of Sir Gilbert Gerard and Anne Radcliffe.
[1] He was educated in Brazen Nose College, Oxford, he matriculated (entered) on 24 November 1609, aged 14, and was awarded his B.A.
[3] He travelled in foreign countries and became a Roman Catholic while in Rome (having been brought up a puritan).
[2] He returned to England and was knighted on 27 July 1639 by King Charles I at Berwick.
[4] In 1640 he was a Lieutenant-Colonel in the English army commanded by Earl of Northumberland (during the Second Bishops' War with Scotland).