In 1603 Winwood was sent to The Hague as agent to the States-General of the United Provinces, and was appointed a member of the Dutch council of state on the basis of the Treaty of Nonsuch.
As ambassador, Winwood publicly intervened in the Vorstius affair, and secretly sided with the Contra-Remonstrants in the religious conflicts that engulfed the United Provinces during and after his embassy.
Having returned to England Sir Ralph became secretary of state and Privy Councillor from 1614 until his death and a Member of Parliament (MP) for Buckingham.
Spanish envoys at Court of St James's made several written complaints about the secretary's share in this undertaking to the king at Whitehall Palace.
John Chamberlain described improvements at Ditton Park in August 1617 made by Winwood and his wife, including a new dovecote, a spring and conduit, fair ponds, damming and filling in the old moat, planting an orchard, and setting out a walled garden with arbours.