Governor Jan Pieterszoon Coen found van Diemen to be a talented official and by 1626 he was Director-General of Commerce and member of the Council for the Indies. In 1630 he married Maria van Aelst. A year later he returned to the Netherlands as Admiral on the ship Deventer. In 1632 he returned to Batavia and in 1635 he was appointed Governor-General of the Indies, his appointment taking effect on 1 January 1636.
Van Diemen's nine years as Governor-General were successful and important for both the colony and the commercial success of the East India Company. He devoted much of his energy to expanding the power of the company throughout Asia. Under his rule Dutch power was established in Ceylon (now Sri Lanka).
Van Diemen is best remembered for his efforts to foster exploration of the land to the south, Australia. He appointed Frans Visscher to draw up a plan for new discoveries. Visscher mapped out three different routes and van Diemen decided in August 1642 to send Abel JanszoonTasman in search of the Great South Land.
In November 1642 Tasman's ship spotted land, and soon found a large territory which Tasman named Van Diemen's Land in honour of his patron. This was the name the island retained when British settlement began there in 1803, and under which it became a byword for horror in England because of the severity of its convict settlements such as Port Arthur and Macquarie Harbour.
The name Van Diemen's Land acquired such odium that when the colony became self-governing in 1855 one of the first acts of the new legislature was to change its name to Tasmania. But the old name lingered for many years - Tasmanians were referred to as Vandemonians until the turn of the century.
Anthony van Diemen died in April 1645. The company granted his wife a large pension and she retired to the Netherlands. Her name is perpetuated in the name of the northernmost tip of New Zealand, Cape Maria van Diemen. It was named by Tasman in 1643.