It signals the end of a successful four-year reign, the highlight of which was the Women's Basketball Championship win in 2015.
Marshall had two main reasons for quitting.
''It's really Otago's only premier team now and I don't think it's fair that I hog it,'' he said.
''There's plenty of good coaches in Dunedin that deserve an opportunity to coach our premier team in a national competition.
''I think that's important because we've got some good coaches in Otago.
''And I found it quite challenging this year with work commitments, so I think it's just a good time.''
Marshall, who works at Sky Television, said the 2015 title win was special, and it had been fantastic to be involved with the team.
He had coached a lot of teams throughout the years, including two stints with the Nuggets.
However, he put the Gold Rush at the ''top of list'' when it came to understanding how a team should operate.
That was something he said existed when he began and he tried to not to interfere with.
''It's just been one of those teams that every now and then you get lucky as a coach and you come across a group that is really enjoyable to be around off the court and on the court and at trainings.
''I've had four years of thinking 'if that's the last team I coach, I'll be pretty happy'.
''I've had it probably once or twice before that you get a group that just get it.
''They know how to train hard, they play hard and they're just a really good group of motivated people off the court as well.
''I've really enjoyed it; it's been really good for me as well.''
He said his relationship with assistant coach Dean Ruske - who had also stepped aside - had been key.
''Me and Dean understand each other really well. We can say whatever we like to each other and he's been fantastic and it's made it even more enjoyable really.
''Dean shows quite a lot of passion and I tend to show not a lot of emotion on the sideline.
''I tend to keep things very calm and Dean can have the fire in the belly.
''The girls actually quite often say they enjoy the opposites.
''We really knew each other really well when it came to basketball, so it was just a really good working partnership really.''
Marshall was unsure what he would do now, although he hoped to remain involved in basketball and thought he would continue coaching the Ajax club team.
Spending more time at home would probably be on the agenda too, as coaching the Gold Rush had been a big-time commitment.
Basketball Otago will advertise for a replacement for Marshall.
