Ludik, who turned 30 on Saturday, joined Ulster from French side Agen in 2014. The versatile backline star signed a one-year extension earlier this year and he will qualify to play for Ireland next summer.
He enjoyed a fine start to the 2016/17 season and was rewarded for his superb form with the Kingspan Player of the Month accolade for September.
Ludik is currently out of action due to a fractured cheek bone suffered in the game against Connacht earlier this month and he is likely to return by the end of November.
Commenting on his new deal, Ludik said: "I'm thrilled to be extending my stay at Ulster. Myself and my family really enjoy Belfast and we feel very much at home here.
"Everything about Ulster Rugby is first class; the stadium, the training facilities, the players and coaches, the medical care and the supporters.
"There is a brilliant vibe amongst the squad and everyone is working hard to try to achieve success this season. Once I return to fitness, I'm looking forward to contributing to the team this season and for the following three years."
Director of Rugby, Les Kiss, was understandably delighted with the news:
"Keeping Louis on our roster is a major boost for us. He is an outstanding guy who gives 100% to the cause and adds so much value both on and off the pitch. He is a great influence on the squad and he also does some great work in the local community.
"His form at the start of this season has been absolutely brilliant and I'm looking forward to seeing him deliver for us over the next few years."
