Vermaelen joined the Ajax youth academy in 2000 and won the 2003–04 Eredivisie title in his first season with the club. He had a loan spell with RKC Waalwijk before rejoining Ajax and winning the KNVB Cup and Johan Cruyff Shield. After Klaas-Jan Huntelaar's departure in 2009, he served as club captain for the remainder of the season. He joined Arsenal in 2009 and was included in the PFA Premier League Team of the Year for that season. Following Robin van Persie's transfer to Manchester United in August 2012, he was named club captain but found first team opportunities limited due to the success of Arsenal's new first-choice defensive partnership of Per Mertesacker and Laurent Koscielny. In August 2014, he completed a £15 million transfer to Barcelona in La Liga.