The 31-year old has penned a three-year deal with the A-League champions, moving down under after spending last season in his homeland with VVV-Venlo.
Prior to that, Seip spent time in the UK with Bradford City, Plymouth Argyle, Charlton Athletic, Sheffield United and Blackpool, which came after stints with Heerenveen and Veendam. He is now looking to continue his career by achieving success in Australia.
"This is a major decision in my life as I have to move my whole family over to Australia," Seip said.
"But it was quite an easy decision to make. I spoke to (Mariners midfielder Nick) Montgomery and he said life is amazing, that football in Australia is on the up, and that the Mariners are the current A-League Champions.
"My wife is also close friends with Nick's wife and we have been in contact since talking about Australia. We know a lot about the Club and the area already, and that's why it was so easy to make the decision."