[1][2][3] His parents, both born and raised in Netherlands, moved to Spain in 1978 and settled in Sabadell, where his father Paulus Wildeboer became the head coach of the local swimming club, called Club Natació Sabadell.

Both Aschwin and his older brother, Olaf, a freestyle swimmer, represented Spain at the 2004 Summer Olympics.

Aschwin swam again for Spain in the 2008 Summer Olympics, achieving a new Spanish record in the 100 m backstroke (53.51) and finishing seventh.

On 21 December 2008, while swimming at the Spanish Short Course Championships, Wildeboer broke the men's 100-meter backstroke world record with a time of 49.20 seconds—0.13 seconds faster than the previous world record set by Stanislav Donets.

On 1 July 2009, in the Mediterranean Games held in Pescara (Italy), Wildeboer broke the men's 100 m backstroke long course World Record with a time of 52.38—0.16 seconds faster than the previous world record set by Aaron Peirsol in the Beijing Olympics the previous year.