In his debut season he helped the province reach the knock-out stages of both the Magners League and Heineken Cup.
His performances did not go unnoticed as he picked up the Supporters Club Player of the Season award and the Ulster Rugby Personality of the Year award. Both awards highlighted his popularity and paid tribute to his work both on and off the pitch.
The 2007 Rugby World Cup winner continued his excellent form the following season as he took over the captaincy and guided Ulster on another memorable Heineken Cup run, this time to the final at Twickenham where Leinster secured a third European Cup title.
Progress has continued this season with Ulster winning 17 of 19 competitive games under Muller's leadership.
The squad has cemented its place at the top of the RaboDirect PRO12 table with an 11-point cushion over second-placed Glasgow Warriors, and qualified for the Heineken Cup knock quarter-finals for a third consecutive year.
"The contract extension has been in the pipeline for a while now and I'm delighted to get it signed. I've had a great time at Ulster so far, three years have flown by and I'm really looking forward to a fourth year," said Muller.
"Ulster Rugby has gone through some wonderful times over the past couple of years and it's brilliant to be part of that.
"The players and backroom 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."
He added: "We've done brilliantly so far this season but the next eight to twelve weeks are obviously going to define the season. The important stuff is coming up now.
"We've got the massive Heineken Cup game on April 6 against Saracens, but there's everything to play for in the PRO12 as well."