"If Ian's healthy, he's going to start Opening Day," Gibson said. "Why wouldn't he?"
Kennedy went 21-4 with a 2.88 ERA in 33 starts last year while finishing fourth in the National League Cy Young Award race.
The right-hander got a no-decision in Arizona's Opening Day win against the Rockies last season, his first Opening Day start.
"He deserves it," Gibson said. "If he's throwing the ball good, that will be the case. If he isn't, I'll change my mind. If I think it's better that he doesn't start Opening Day, I'll change my mind, but if everything goes according to plan, he'll be on the mound."
Gibson joked that he made his decision after Kennedy edged out fellow starter Daniel Hudson in a fielding competition Tuesday. When the contest came down to Kennedy and Hudson, reliever David Hernandez yelled out, "Winner starts Opening Day."