It's the second deal the two clubs have made in a month and sends another Cleveland first baseman to the Mariners.
Seattle, in last place in the AL West but only 3½ games behind the division-leading Los Angeles Angels, got first baseman Eduardo Perez in a deal for minor-league infielder Asbrudal Cabrera on June 30.
Broussard hit .321 with 13 home runs and 46 RBI in 88 games with the Indians but was spotty defensively and committed seven errors.
He won't need to worry about defense in Seattle with Richie Sexson at first base for now. Seattle general manager Bill Bavasi said Broussard is being acquired to be a DH against righties exclusively.
"I take pride in playing first base, I love it and will continue to work at it. But I realize at this point of the season it's a role I'm going to have on the team," Broussard said. "I know long-term I'm a first baseman but for now I'll do what I have to do to get in the lineup."
Cleveland will send cash to the Mariners to cover a portion of Broussard's salary. The Indians will receive a player to be named by Aug. 31 to complete the deal.
Broussard and Perez started the season in a platoon at first base for Cleveland, which has underachieved following a 93-win season in 2005.
Indians general manager Mark Shapiro, who dealt closer Bob Wickman to Atlanta last week for a minor-league catcher, said six teams were interested in Broussard.
"He was having a great year. Benny is a guy who's always had streaks where he showed potential," Shapiro said. "I still think Benny's potential is even greater."
Choo has spent most of this season at Triple-A Tacoma, where he hit .323 with 13 home runs and 48 RBI. He played in four games for Seattle between July 3-13, going 1-for-11.
The lefty hitter will join the Indians immediately and start in right field against right-handed pitching. He will also spend some time in left field, Shapiro said.
"This player is a good complement to this club and the club we hope to build in the future," Shapiro said. "This is a guy who has hit every single place he's been."
Choo stole 26 bases in 30 attempts at Tacoma and was picked for the Pacific Coast League's All-Star team. He was a member of Korea's provisional roster for the World Baseball Classic in March.
"Over time, he certainly has the athleticism, speed and the arm to be an above average corner outfielder," Shapiro said.
The Mariners now have three first basemen on their roster in Sexson, Broussard and Perez, who is hitting .294 with a home run and five RBI in 17 at-bats since joining Seattle.
Seattle will travel to Cleveland to open a three-game series with the Indians on Friday night.
"We hope [Broussard] goes on after the next three games to do good things," Shapiro joked.