Winker and third baseman Eugenio Suarez are headed to Seattle in exchange for right-handed pitcher Justin Dunn, outfielder Jake Fraley, 2019 second-round pick Brandon Williamson and a player to be named later.
On a loaded offense in Cincinnati last season, Winker was a fixture in the lineup, appearing in 110 games with 423 at-bats. He finished with 24 home runs, 71 RBIs and 235 total bases.
"We're incredibly excited at the chance to acquire two All-Star-caliber players," Seattle general manager Jerry Dipoto said. "Jesse has been one of the premier offensive players in the league over the past two seasons, while Suarez brings a long track record as a power hitter."
Winker, 28, was among two Reds regulars -- Nick Castellanos (.309) was the other -- to finish with a batting average over .300 (.305). The former first-round pick of the Reds made his major league debut on April 14, 2017.
In Winker, the Mariners will receive a needed, steady hitter who can cover a lot of ground in the outfield. Seattle, at 90-72, finished in second place in the American League West last season, but with just 697 runs scored, the Mariners were second to last in the division in offense.
In Suarez, Seattle landed some pop at third base. He appeared in 145 games for the Reds last season, launching 31 home runs, second on the team. He finished with 79 RBIs but just a .198 average.
"Our goal is to reach the postseason this year," Dipoto said. "And we feel that these additions give us the depth and impact in our lineup necessary to compete for one of those spots.''
Winker shined against right-handed pitching last season en route to his first All-Star Game appearance. The Reds challenged for a postseason berth in the National League most of the season before their pitching ultimately could not catch up to their offense. Cincinnati finished at 83-79, in third place in the National League Central, 12 games behind the division champion Milwaukee Brewers.
On Sunday, the active Reds shipped right-hander Sonny Gray to the Minnesota Twins. Cincinnati included minor league right-hander Francis Peguero in the deal for Twins pitching prospect Chase Petty, who was Minnesota's first-round draft pick last year.
Gray, 32, a two-time All-Star, went 7-9 with a 4.19 ERA and 155 strikeouts over 135⅓ innings in 26 starts last season, his third with the Reds.