If the trade is completed as planned, Kotchman would be penciled in as the Mariners' starting first baseman.
Hall, an infielder-outfielder, was acquired by the Mariners from Milwaukee in August. He started at short for the Brewers in 2006, but also has played second and third and all three outfield positions and figures to be Boston's top infield reserve as Jed Lowrie, who is recovering from a wrist injury, is expected to start the season in Triple-A Pawtucket.
Hall hit 35 home runs in 2006 for the Brewers, but a total of 37 since, including eight last season, in which he batted just .201 in 110 games between the Brewers and Mariners.
Hall's inclusion in the deal was first reported by the Seattle Times.
The Red Sox are still looking for ways to part with third baseman Mike Lowell and move forward with Adrian Beltre at third base and Kevin Youkilis at first. The Red Sox have reached an agreement with Beltre, who must pass a physical for his one-year, $10 million contract to become official. Beltre is expected in Boston by the end of this week, most likely on Thursday, to take that physical, according to an industry source.
Kotchman, who split 2009 with the Red Sox and the Atlanta Braves, hit .268 with seven home runs and 48 RBIs. He batted .282 in 87 games with the Red Sox, with whom he hit six of his seven homers. The Red Sox obtained Kotchman last season in a trade that sent Adam LaRoche to Atlanta.
He is a career .269 hitter in six seasons with the Red Sox, Braves and Los Angeles Angels.
The proposed deal suggests Seattle won't bring back slugging first baseman Russell Branyan. The Mariners fear the free agent might not be completely healed from a disk issue in his back from late last season and may not be worthy of the multiyear contract he wants.
The person familiar with the trade talks also told the AP that the Mariners are likely to announce in the coming days a contract extension with center fielder Franklin Gutierrez.
Gutierrez's agent, Wil Polidor, did not immediately return a message seeking comment Tuesday evening.
Polidor told MLB.com the four-year deal worth in excess of $20.5 million, with an option for a fifth season, is "90 percent done" and that "we are just waiting on Seattle."
Gutierrez, who played his first four major league seasons for the Indians, then had his best year with Seattle. He set career highs with a .283 batting average, 18 home runs and 70 RBIs -- and he wowed his new team with far-ranging defense and a constant stream of highlight-worthy plays.
Next to perennial Gold Glove right fielder Ichiro Suzuki, the smooth Gutierrez gives the Mariners one of baseball's best outfield defenses.
Signing him to a multiyear deal and acquiring Kotchman, who is less of a power hitter but is eight years younger and a better defender at first base than Branyan, would fit second-year general manager Jack Zduriencik's plan of rebuilding the rising Mariners through youth, defense and pitching.
Information from ESPN The Magazine senior writer Buster Olney, ESPNBoston.com's Gordon Edes and The Associated Press was used in this report.