He'll make his first start for San Diego in Sunday's finale against the visiting New York Yankees, who were the first to trade the right-hander nearly four years ago.
Kennedy, the 21st overall pick of the Yankees in 2006, went 1-4 with a 6.03 ERA in 12 starts and two relief appearances for New York from 2007-09 before being traded to Arizona in December 2009 in the three-team deal that brought Curtis Granderson to the Bronx.
Kennedy had a career season in 2011 for the Diamondbacks by going 21-4 with a 2.88 ERA before winning 15 games in 2012, but he hasn't been able to find that form this year.
Arizona traded Kennedy (3-8, 5.23 ERA) to San Diego on Wednesday for left-handed reliever Joe Thatcher, a minor leaguer and a draft pick.
"You work so hard with the team you're with and then you get traded," Kennedy told the team's official website. "But I'm excited because I got to come to a team that I'm familiar with, a division that I'm familiar with -- kind of a little mixed emotions."
Kennedy also finds it a bit strange that he'll be making his first start with the Padres against the team he came up with.
"It's kind of ironic," Kennedy said. "Kind of (have) come a little full circle."
San Diego starters rank 14th in the NL with a 4.59 ERA, a mark Kennedy looks to help improve as he faces a New York team that won Saturday's contest 3-0.
Granderson, who came off the disabled list before Friday's 7-2 loss to the Padres, hit a two-run homer in the seventh.
"I've talked about how Curtis can change the complexion of the game really quickly, and that's what he did," manager Joe Girardi said. "That's why I put him in the four slot, because of how he can change a game. It's really nice to have him back.''
The Yankees (57-52) will again be without Derek Jeter, who has a sore right leg and also was held out of the lineup Saturday. Girardi said Jeter needs to rest for at least another day.
"It's a concern of ours and we've got to try to get him healthy,'' Girardi said.
San Diego (51-60) had won five of six prior to Saturday's defeat. It has been held to two runs or fewer six times over its last 10 games.
The Padres will look to bounce back while facing Kennedy's former teammate of three years, Phil Hughes, on Sunday.
Hughes (4-9, 4.58), much like Kennedy, has been struggling this season. He's lasted fewer than five innings seven times, including last Sunday when he allowed five runs and nine hits in four frames of New York's 6-5 win over Tampa Bay.
"I wasn't able to hold a lead twice, something us starters take a lot of pride in," Hughes said. "To not be able to do that is disappointing."
The right-hander has never faced the Padres, who have lost 12 of 15 all-time meetings - beginning with the Yankees sweeping the 1998 World Series.