Claes was the fifth surviving son of Wolfert I van Borselen and his wife Sibilie.

Right after the assassination, a number of his allies, as well as his younger sons Frank and Claes were imprisoned in Holland.

[3] Later that year Frank and Claes were allowed to leave their prison under guarantee from their allies that they would soon be delivered back.

[5] Also on 11 October Jan Mulart van Borselen gave the guarantee that he would return to his prison in Delft, and would deliver Frank and Claas children of his brother Wolfert, and Pieter son of Floris.

[6] In 1300 the events led to war between the Count of Holland and the Van Borselen clan, in which Flanders became involved.

In 1303 Claes was mentioned in the last will of his older brother Sir Hendrik Wisse van Borselen, knight.

[8] In May 1309 there was a reconciliation about Wolfert I's death in 1299, and the execution of some of his killers by the Van Borselens at Veere in 1300.

[9] On 30 May 1316 Wolfert II made a contract about his grandfather's estate with his brothers Sir Florence, Frank and Claes van Borselen.

He (wrongly) dubbed him Lord of Brigdamme, Zoutelande and Koudekerke, and founder of Popkensburg Castle in the lordship of Sint Laurens.

He noted that during Claes' lifetime, not a single Van Borselen owned land in Brigdamme.

[16] Meerkamp van Embden also annulled the claim that Claes I had founded Popkensburg Castle.

During the Hook and Cod wars, Claes pledged loyalty to Margaret II, Countess of Hainaut in January 1351.

The rebellion led to the lost May 1351 Battle of Veere, but there are no indications that this defeat had any serious consequences for the Borselens.