The 32-year-old international, who signed with the province three years ago, said he is looking forward to another season at Ravenhill.
"Ulster Rugby has gone through some wonderful times over the past couple of years and it's brilliant to be part of that," he said.
"The players and back room staff have done an amazing job over the past three years and it's an exciting place to be. Everybody is really happy being part of this squad and this environment and I'm no different. We're on the right track and hopefully we can keep on going and win some silverware."
Muller has been capped 24 times by South Africa and has played an influential role at Ulster since joining the squad, including guiding the team on a memorable Heineken Cup run last season which saw them reach the final against Leinster at Twickenham.
Progress has continued this season with 17 out of 19 competitive wins under his leadership.
Muller continued: "We've done brilliantly so far this season but the next 8 to 12 weeks is obviously going to define the season.
"The important stuff is coming up now. We've got the massive game on 6 April against Saracens, but there's everything to play for in the PRO12 as well."