The 31-year-old has arrived at Franklin's Gardens after the conclusion of the Japanese Top League where he has been playing for the NTT Docomo Red Hurricanes.
Brussow can play across the back row and will inject plenty of experience into the Saints' ailing pack.
He previously earned 23 caps for South Africa, representing the Springboks in both the 2009 series against the British & Irish Lions and the 2011 Rugby World Cup.
Having signed back in September, the Bloemfontein-born star says he is excited about his spell in the Premiership.
"It's great to be here," he said. "It's been a few months now that I've been waiting to come, and I'm very excited to get to work on the training field and get involved with the squad.
"I really enjoyed my time in Japan but I am at a stage in my career where I need a new challenge, and coming to Europe and playing in some of the best competitions in club rugby is something that is very special.
"The Saints is a fantastic Club with big traditions and I'm really excited to get to know all the English cultures and learn what the Aviva Premiership is all about.
"There is a lot of talent in the squad and I can't wait to get out and start playing with them.