This was done against great opposition and amid fierce debate.
Soon afterwards Barneveld was vehemently urged by the nobles and regents of the cities of Holland to accept the post of Advocate of that province.
After repeatedly declining the arduous and most responsible office, he was at last induced to accept it.

He did it under the remarkable condition that in case any negotiation should be undertaken for the purpose of bringing back the Province of Holland under the dominion of the King of Spain, he should be considered as from that moment relieved from the service.
His brother Elias Barneveld succeeded him as Pensionary of Rotterdam, and thenceforth the career of the Advocate is identical with the history of the Netherlands.

Although a native of Utrecht, he was competent to exercise such functions in Holland, a special and ancient convention between those two provinces allowing the citizens of either to enjoy legal and civic rights in both.

Gradually, without intrigue or inordinate ambition, but from force of circumstances and the commanding power of the man, the native authority stamped upon his forehead, he became the political head of the Confederacy.

He created and maintained a system of public credit absolutely marvellous in the circumstances, by means of which an otherwise impossible struggle was carried to a victorious end.
When the stadholderate of the provinces of Gelderland, Utrecht, and Overyssel became vacant, it was again Barneveld's potent influence and sincere attachment to the House of Nassau that procured the election of Maurice to those posts.