Willem van Outhoorn (or Oudthoorn) was born on 4 May 1635 at Larike on Ambon Island in Indonesia.

On 17 December 1690 van Outhoorn was appointed Governor-General of the Dutch East Indies, taking over from Johannes Camphuys on 24 September 1691.

After ten years, the Seventeen Lords (Heren XVII) granted his wish to be honourably relieved of his duties, but it was 15 August 1704 before he could hand over all his official functions to his successor, Joan van Hoorn.

Such requests were generally not allowed, for fear that retired governors would interfere with the work of their successors.

As the VOC did not recognise his son as successor, a long war broke out just before Van Outhoorn left office.

His son-in-law Joan van Hoorn, married to his daughter Susanna, succeeded him as Governor-General.