The South African lock made his international debut in the Rugby Championship last year and has enjoyed a long and storied career with Super Rugby side The Lions.
He will join fellow Springbok Ruan Pienaar and follow in the wake of retiring skipper Johann Muller at Ulster, who are both into their fourth seasons in the RaboDirect PRO12 having made a huge impact with the Irish province.
And van der Merwe insists he is relishing the chance to expand his horizons at Ravenhill for at least the next two years.
"I'm 31 and I've signed a two-year deal, and my wife and I feel that it is the right time for a career change," van der Merwe said.
"Hopefully we can experience a new culture and lifestyle. It's been something we've discussed for a while now and there really hasn't been a time to do it before now.
"There are a few South Africans up there, so I'm looking forward to meeting up with them and making new friends in a different culture."
Follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up to our newsletter for regular updates on the RaboDirect PRO12
Guinness PRO12 Ulster News
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland
63x46.png){kind=logo}