Kotsay is the seventh person to hold the job since spacious Petco Park opened in 2004. By comparison, the Padres have had only two managers since then, Bruce Bochy and Bud Black.
Kotsay replaces Phil Plantier, who was fired after the end of last season. The Padres' offense was abysmal in 2014, particularly in the first half.
"I'm not really worried about job security. In my role, I look at it as an opportunity to get back into the game that I love, the opportunity to be part of a great coaching staff and help lead this group of hitters in the direction we foresee," said Kotsay, who had two stints with the Padres.
It will be the first professional coaching job for Kotsay, who turns 39 on Tuesday. After retiring from his playing career following the 2013 season, the outfielder spent last season as a special assistant to the Padres' general manager.
Kotsay said he had 12 different hitting coaches in his 17 big league seasons.
"It's a difficult task. It's a role that in some regards is not necessarily rewarding," he said. "Being recently retired ... my connection to the game and the players that I'm going to be leading is very close, very new, very fresh. I think that I will have an understanding of what they're going through as players, based on my career, and the different roles that I played as an offensive player on different teams, the successes, the failures. I'll be able to reflect on what they're going through and things like that."
Kotsay played parts of 17 big league seasons with the Marlins, Padres, Athletics, Braves, Red Sox, White Sox and Brewers. The left-hander had a career average of .276, with 127 home runs and 720 RBIs in 1,914 games.
Being the Padres' hitting coach has largely been thankless and short-lived for Kotsay's predecessors.
Plantier replaced Randy Ready, who was fired a day after the Padres finished last in the NL West at 71-91 in 2011. The other Padres hitting coaches during the team's time at Petco Park have been Dave Magadan, Merv Rettenmund, Wally Joyner and Jim Lefebvre. All were fired except Joyner, who resigned late in the 2008 season, before he could be fired.
When Plantier was fired, the Padres said his assistant, Alonzo Powell, would return to the staff.
As for getting the Padres to hit better at Petco Park, Kotsay said he'll tell the players "to use the field for the way it is. There's a lot of open space out there in the outfield and you will reward yourself when you take a positive at-bat. In the long run it's about scoring runs. When we score three or four runs in Petco Park with the pitching staff we have, it will present opportunities to win games. Last year's club, in the second half of the season, made improvements. We're going to continue to hopefully build on those improvements in spring training, with the philosophy being that we as a group are going to be better. That's the focus."
Black managed Kotsay in his final two big league seasons, 2012-13.
"I felt we had a guy who was ready to make an impact on our major league club immediately," Black said. "I think his personality, his competitiveness, his knowledge of hitting, is something that will complement Alonzo Powell and he'll also fit right in with our major league staff. It makes a lot of sense."
The Padres have missed the playoffs for eight straight seasons. They finished third in the NL West last season at 77-85, 17 games behind the division-champion Los Angeles Dodgers.