The deal has a $3.5M average worth per year, a source told ESPN's Pierre LeBrun.
Eller was scheduled to have an arbitration hearing on Friday.
Eller took to Twitter to announce the news:
Very happy to be a part of the Montreal Canadiens for 4 more years! @CanadiensMTL
- Lars Eller (@Eller_89) July 24, 2014
"We are very pleased to have agreed upon a long term agreement with Lars Eller," general manager Marc Bergevin said in a statement. "He is an important part of our group of young veterans."
Information from The Associated Press was used in this report.