Juan Soto, one of this generation's finest hitters, has officially joined the New York Mets on a reported 15-year, $US765 million (A1.2m) contract, the Major League Baseball team has confirmed.

Soto, who spent the 2024 season with the crosstown rival New York Yankees, is now the face of a Mets franchise seeking their first World Series title since 1986, and their championship odds have significantly improved since reports of the deal surfaced on December 8.

"This is a seminal moment in franchise history," Mets owners Steve and Alex Cohen said in a statement.

"Juan Soto is a generational talent. He is not only bringing staggering historical statistics with him but also a championship pedigree. Our Amazin' fan base is very excited to welcome Juan to Queens. Congratulations, Juan."

The contract, which was finalised on Wednesday after a physical, contains a full no-trade clause, a $US75 million ($A117.5m) signing bonus, an opt-out after five seasons and no deferred money, according to MLB.com.

It is the biggest contract in MLB history, eclipsing the 10-year, $US700 million pact the Los Angeles Dodgers signed Shohei Ohtani to last winter.

A precocious hitting talent, the 26-year-old Soto enjoyed a career year with the Yankees in 2024 as he set career highs in a number of categories, including runs, hits, home runs, total bases and extra-base hits.

The Yankees had acquired Soto last December as part of a blockbuster seven-player trade.

Soto and Aaron Judge formed a dynamic duo in the Bronx and helped power the Yankees to their first World Series appearance in 15 years. They lost to the Dodgers 4-1 in the best-of-seven championship series.

The Mets made a surprise run to the 2024 National League Championship Series in their fourth season under billionaire owner Steve Cohen and their success in luring Soto away from the Yankees came as something of a surprise.

The Boston Red Sox, Toronto Blue Jays and Dodgers were also reportedly in the running for Soto.