Smoltz, whose signing is to be announced formally Tuesday, is the only pitcher in baseball history with 200 wins and 150 saves. He attended the Boston Celtics' 115-109 overtime win over the Toronto Raptors on Monday night and was interviewed during a break in the action.
"It's going to be [as] a starter," he said when asked how the Red Sox would use him. "They're going to make sure that I'm ready to not only pitch, but pitch strong down the stretch and into the playoffs because that's what I like to do."
The Red Sox scheduled a news conference for 10 a.m. Tuesday to announce the signing.
Preliminary agreement was reached last week on the deal, believed to be one year and $5.5 million, with a possible added $5 million in performance bonuses. The deal was expected to be contingent on Smoltz passing a physical on Monday.
The Red Sox already had Josh Beckett, Jon Lester, Daisuke Matsuzaka and Tim Wakefield in the rotation and added former Los Angeles Dodgers right-hander Brad Penny last week. Youngsters Clay Buchholz and Justin Masterson also could figure in that group.
The 41-year-old Smoltz has said he feels healthy enough to pitch at least one more year.