Kotsay is hitting .275 this season with one home run and nine RBIs in 102 at-bats. Kotsay, who will turn 37 on Dec. 2, is 9-for-31 (.290) as a pinch-hitter this season.
Going back to Spring Training, Kotsay has been a positive influence in the clubhouse and a mentor of sorts to several players on the roster who are low in service time.
"Kotsay has done a very good job in a number of areas, primarily as a player," said Padres manager Bud Black. "He's done a nice job when he gets his starts, he's a very valuable pinch-hitter from the left side. He's won a couple games for us with some big hits late. That's the main thing -- he's still providing good play.
"And he's a great sounding board for our players. He's a guy that there's no doubt on our club is needed with the amount of younger players who can seek him out for counsel."
It's a role Kotsay has embraced since the start of Spring Training.
"It's not about the words you speak ... Tt's about your actions, the way you go about handling yourself as a professional day in and day out, both on and off the field," Kotsay said earlier this season.
"Hopefully I can come across in a positive manner and that flows over and the guys learn that you've got to put in the work and effort to get the result on the field."
Kotsay originally signed a one-year deal with the Padres worth $1.25 million last Nov. 15.
Kotsay's extension comes on the heels of two moves general manager Josh Byrnes made in July, when the team gave outfielder Carlos Quentin a three-year deal for $27 million and closer Huston Street a two-year deal for $14 million.
Going into Sunday's series finale in Pittsburgh, Kotsay had made 15 starts in left field, five starts in right field and two starts at first base.
In the span of a week earlier this season, Kotsay had a pinch-hit two-run double in the eighth inning in a 2-1 victory over the Nationals, and then, five days later, he had a two-run pinch-hit home run in the eighth inning which helped the Padres to a 2-0 victory over the Brewers.
Kotsay, in his 16th Major League season, also played for the Padres from 2001-03. He was a first-round pick of the Marlins (ninth overall) in 1996 out of Cal State Fullerton.