The outfielder, who turns 28 in October, was acquired by the Dodgers from the Boston Red Sox on Feb. 10 along with pitcher David Price for three players.
Betts had agreed to a $27 million, one-year deal with the Red Sox, a salary that has been reduced to $10 million in prorated pay because of the shortened season.
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His deal is baseball's second-largest in total dollars behind the $426.5 million, 12-year contract for Los Angeles Angels outfielder Mike Trout covering 2019-30. Betts' average salary of $30.42 million trails Gerrit Cole ($36 million), Trout ($35.5 million), Stephen Strasburg and Anthony Rendon ($35 million each), Zack Greinke ($34.4 million), Justin Verlander $31.3 million), and new teammates Price and Clayton Kershaw ($31 million each).
A four-time Gold Glove winner, Betts won the 2018 AL MVP award en route to Boston's World Series title. He hit .295 with 29 homers and 80 RBIs last year, down from a major league-leading .346 average with 32 homers and 80 RBIs in his MVP season.
His agreement leaves catcher JT Realmuto, outfielder George Springer, shortstop Marcus Semien and pitchers Trevor Bauer and Marcus Stroman as the top players headed toward free agency.