In 2007, he toured the Netherlands and served as a player-coach for Hermes Cricket Club, taking charge of the age group and main team.

[10] McCullum played in a number of overseas Twenty20 tournaments from 2010 for sides including Lancashire, Pune Warriors India, Sunrisers Hyderabad, Sydney Sixers, and Glamorgan.

[11][12][13] In 2010, he replaced Shoaib Malik as Lancashire's overseas player for the T20 Blast[14] and was selected by Sydney Sixers for the 2011–12 Big Bash League season.

[15] He was part of the Sydney team which won the 2012 Champions League Twenty20, taking three wickets in the final against Highveld Lions.

[31] Although he was named in the final squad of 15 in 2015 Cricket World Cup, he was mostly used as a substitute fielder to Daniel Vettori.

[32] In 2015, McCullum announced he will retire from all forms of cricket at the end on the 2015/16 Southern Hemisphere summer season.

[33] Prior to concentrating on his cricketing career, McCullum played association football as a striker for Caversham AFC, winning the team's golden boot award in 1999 by scoring 19 goals in the FootballSouth Premier League.