Kapler was fired by the Giants with three days left in the 2023 regular season after the team failed to make the playoffs for a second straight year. He had a 295-248 record over four seasons with the Giants, but his only year of guiding the team to a winning record was 2021, when San Francisco won a franchise-record 107 games and the National League West title.
San Francisco lost in the NL Division Series that year in five games to the Los Angeles Dodgers then went 81-81 in 2022. The Giants were 78-81 at the time of Kapler's firing.
Kapler, 48, also managed the Philadelphia Phillies from 2018-19, going 161-163.
Once his hiring is announced, Kapler will be one of four assistant general managers under new president of baseball operations Peter Bendix, along with Brian Chattin, Daniel Greenlee and Oz Ocampo. The Marlins brought in Bendix last month to lead the organization.
The Miami Herald first reported news of Kapler's impending hire.
Information from The Associated Press was used in this report.