Montag filed for divorce in Santa Monica, Calif., Superior Court, says People.com. She sought legal separation from Pratt last May.
"Heidi has amended her petition for separation and today has filed a petition for dissolution of marriage from Spencer Pratt," Montag's lawyer tells the site. "The couple has agreed they would like their divorce to be finalized in a timely manner in an out-of-court settlement. Both parties are amicable with each other and over the possibility of finalizing their divorce."
The controversial reality couple officially tied the knot in Pasadena, Calif., in April 2009.