He was born in London on 17 October 1704, a younger son of Hans Willem Bentinck, 1st Earl of Portland, who died when Willem Bentinck was only five years old. His guardian became Johan Hendrik, Count van Wassenaer-Obdam. As all the British properties had been inherited by his half-brother, there were no prospects for him in England and at fifteen he was sent to Holland to start a political career. Later on he would inherit the Dutch properties. 
As a young man, to the annoyance of his guardian, Willem Bentinck enjoyed himself greatly in The Hague and ran up enormous debts. In the long run his guardian was forced to make arrangements for the repayments. In his twenties he was determined to marry Countess Charlotte Sophie von Aldenburg, heiress of Varel, Kniphausen and Doorwerth. However, she preferred an unattainable German prince and demanded that he would at least become a Count of The Holy Roman 
Empire. 
Emperor Karl VI, on 29 December 1732, elevated him and, as Count Willem Bentinck, he was accepted by Charlotte Sophie and married her on 1 June 1733. They became the parents of two sons. However, Charlotte Sophie didn't bring prosperity, as a lot of money was owing on her properties and her debts exceeded his. Their marriage was an unhappy one and in 1740 they separated. Her properties were securities for their children and for fourteen years she fought her husband in the courts. On 18 August 1754 she was forced to accept that her main properties went to her sons. 
The most important part of his political career was spent on the restoration of Stadhouder Willem IV. In 1747 Willem IV was at last accepted in Holland and Count Willem Bentinck accompanied the prince on his journey through Holland and Zeeland. However, his political ambitions came to nothing as he was distrusted by the prince's wife. 
Nevertheless, he was capable, honest and a man of principles. On 13 October 1774 he died on his property 'Zorgvliet' near The Hague. 

Source: Leo van de Pas