He was elected Stadholder of Holland, Zeeland, Utrecht, Gelderland and Overyssel, and was appointed Captain-General and Admiral-General of the Union and head of the Council of State.

During practically the whole of his life the prince spent a considerable part of the year in camp, but he was able all the time to keep in touch with home affairs, and to exercise a constant supervision and control of the foreign policy of the State by the help of his wife, and through the services of Francis van Aerssens.

The Court of the Princess of Orange, graced as it was by the presence of the exiled King and Queen of Bohemia, was brilliant and sumptuous, and gave to the reality of power possessed by the stadholder more than a semblance of sovereign pomp.
During her husband's absence she spared no pains to keep him well-acquainted with all the currents and under-currents of action and opinion at the Hague, and was not only able to give sound advice, but was quite ready, when necessity called, to meet intrigue with intrigue and render abortive any movements or schemes adverse to the prince's policy or authority.

The obligations of Frederick Henry to Aerssens were even greater.

The stadholder was at first suspicious of the man, whom he disliked for the leading part he had taken against Oldenbarneveldt.