The league announced Donald's win with the following tweet:
Also, New Orleans Saints defensive end Cameron Jordan, Dallas Cowboys defensive end Demarcus Lawrence, Seattle Seahawks linebacker Bobby Wagner, Minnesota Vikings cornerback Xavier Rhodes and Vikings safety Harrison Smith garnered one vote apiece.
Although he missed the season's first game due to a contract dispute and sat the final contest as a precaution prior to the playoffs, Donald was the league's best defender.
The 2014 first-round draft pick finished with 41 tackles, 11.0 sacks and five forced fumbles for a Rams team that was among the NFL's most improved in 2017.
While the offense went from worst to first in scoring and captured many of the headlines, Donald was a big reason L.A.'s defense finished fourth in sacks with 48.
He was a disruptive force against both the pass and run, and no interior defensive lineman blew up plays in the backfield more often or emphatically than Donald.
He has been named to the Pro Bowl in each of his first four NFL seasons and is now a three-time First Team All-Pro.
After finishing a dismal 4-12 record in 2016, the Rams made a seven-win jump by going 11-5 and winning the NFC West.
Despite getting bounced in the NFC Wild Card Round by the Atlanta Falcons, Donald and the Rams announced they are back to being contenders after 12 consecutive years out of the postseason.
Donald finished fourth in the Defensive Player of the Year voting last year and second in 2015.
The Rams' struggles may have contributed to the fact he fell short in the past, but everything came together in 2017.
Donald's triumph is a rare occurrence, as he became the first player to primarily line up at defensive tackle to be named NFL Defensive Player of the Year since the Tampa Bay Buccaneers' Warren Sapp in 1999.