The 36-year-old all-rounder is not describing his absence from the Otago twenty20 side this season as retirement, but it certainly feels like his career has reached its end.
He had been negotiating to play for the Volts in the Super Smash but was unable to reach an agreement with the Otago Cricket Association.
McCullum retired from international cricket at the end of last season to spend more time with his wife, Vanessa, and the couple's three children, Luke (6), Jake (4) and Tom (2).
The family moved to Auckland last year and McCullum took up a consultancy role with Stellar Recruitment.
''I would have loved to have led the Otago team ... but unfortunately it hasn't managed to work out,'' McCullum said.
''I don't know if it is retirement from all cricket but I won't be playing for Otago this summer.
''With my commitments with work and family life, it does not make sense and would have been almost a little bit selfish to try and do so.
''At the end of the day, it is time to move on and I'm really enjoying the opportunity I've got here with work.
''It is going really well. I've actually got [former Otago players] Roald Badenhorst and Brad Rodden sitting alongside me in the office.
''There is sadness, obviously. I would have loved to have played again. It would have been great to get involved with [Volts coach] Rob Walter and the new set-up down there to try to help some of the guys continue to progress.''
While work commitments and family life formed a major part in his decision, finances also played a role. The offspinner is not ruling out playing twenty20 cricket in the various overseas leagues if the opportunity stacked up but is ''pretty much done here in New Zealand''.
''In order for me to make sure I was performing to the best of my abilities for me and my team-mates, it was going to take a lot of time and hard work to do that and obviously time off work.
''[Finances] obviously come in to it and that is always a factor along with everything else.''
Otago Cricket Association chief executive Mike Coggan said McCullum's leadership, inspiration qualities and cricket ability would be sorely missed but the association had a ''limited amount of funding'' and ''clearly the money side of it was, in the end, the difference between securing and not securing Nathan''.
McCullum made his first-class debut for Otago against Wellington in March 2000. He took four wickets but made an inauspicious start with the bat, compiling two golden ducks.
His average eventually recovered. In 62 first-class games for Otago he scored 2270 runs at 25.79, including one century and 14 half centuries.
He also took 122 at 41.23 wickets but was more effective with the ball in the limited-over formats. He is stuck on 99 one-day wickets, though and needed a further 191 runs to reach 2000 career runs.
But it was T20 cricket in which McCullum really excelled. He stood out with his athleticism in the field and his ability to tie batsmen down. He was also a very handy and explosive middle order batsman.
''I've always been pretty passionate about playing for Otago and the blue and gold is part of me. Otago is [in a development phase] and I'm excited to see what the guys are going to do.
''They are a great bunch of fellows and I'm sure they are going to be pretty successful.''
