All that was left was the physical, and Penny came to Boston and passed that on Thursday.
Now, he can officially go about the process of trying to get back the dominance that led to his back-to-back All-Star appearances with the Dodgers in 2006-07.
"For me, going out there and pitching like that [last year] was embarrassing," Penny said in a conference call. "Like I said earlier to someone else, I was pushing through something I probably shouldn't have, and rest would have helped me out and I would have been a lot better off. That's not the [real] Brad Penny last year, and I know that, and hopefully all the people know that, and Boston, apparently they think that, too. I'm going to go out there and work my butt off and do the best I can. I do feel like I have something to prove."
Penny signed a one-year contract worth a base salary of $5 million, but his deal has innings-based performance incentives that could garner him an additional $3 million.
Why did Penny pick the Red Sox? One of the big reasons is the shoulder program spearheaded by Mike Reinold, Boston's assistant trainer.
"I had heard about the shoulder work he had done from a lot of people," Penny said. "The more I looked into it, the more everybody was telling me this was the best guy. That was a huge factor in my decision and I can't wait to get where I should be. I need to get some strength in my shoulder after last year."
Familiarity was also a factor. Josh Beckett and Mike Lowell, two Red Sox cornerstones, were teammates and friends with Penny on the 2003 World Series champion edition of the Florida Marlins.
"Oh, they were awesome teammates," Penny said. "Me and Josh had a lot in common; we were both younger guys, we both liked to hunt. All three of us won a World Series together. We were really close. That's probably the closest I've ever been to teammates -- that whole Florida team. Mikey Lowell, you're not going to meet a better person. Both those guys go out there and they're fierce competitors, and I can't wait to join them again."
The Red Sox's rotation now appears set. Penny will join Beckett, Jon Lester, Daisuke Matsuzaka and Tim Wakefield. And by May or June, John Smoltz, coming off right shoulder surgery, will be added to the mix. The Sox are expected to officially announce Smoltz's signing next week.
If Penny can get back to the level he was at before last year's dropoff, the Red Sox could have themselves one of the best bargains of the winter.
After posting back-to-back 16-win seasons with the Dodgers in 2006-07, Penny slipped to 6-9 with a 6.27 ERA in 19 appearances in '08. Because of shoulder issues, Penny pitched just four times after June 14.
"Even when I was on the DL, I was playing catch," Penny said. "I never took enough time off without throwing. It's tough when you're competing and you're getting paid a lot of money, and you want to get out there on the mound and be the best you can be, and I was a little stubborn about it and tried to rush myself."
Perhaps John Farrell, one of the most highly regarded pitching coaches in the game, can help Penny round back into form.
"I can't wait," Penny said. "I sat down and talked to him a little bit yesterday, and I'm really looking forward to it. Everybody that I've talked to has been nothing but great to me. I'm really looking forward to working with a lot of great people."
Will Jason Varitek be one of them? The catcher, long lauded for the way he handles pitchers, remains a free agent.
"I've heard a lot about him," Penny said. "I don't know him personally. I've met him a few times. I've heard how prepared he is. A guy like that can make my job a lot easier just by knowing the hitters and knowing my stuff and knowing what I need to throw to each and every hitter. Talking to Mikey Lowell and those guys, they told me there's nobody more prepared. I'd love to throw to him. If it works out, that would be great. If it doesn't, I'd love to throw to anybody out there in Boston."
And with the Red Sox's deep staff, they can be conservative with Penny's usage.
However, Penny, who has already started throwing, has no reason to think he won't be right on schedule when Spring Training begins.
"The goal right now is for everything to be as usual," Penny said. "That's what I'm planning on. I met with them yesterday, and I'll throw my first bullpen [session] when everybody else does."
Penny became a free agent after the Dodgers paid him a $2 million buyout rather than picking up his $9.25 million option.
Penny, 30, is 94-75 in his career, with a 4.06 ERA and 1,032 strikeouts. He has spent his entire career in the National League.
He is another power arm in a rotation that, excluding Wakefield, is packed with them.
When he came to town for his physical, Penny took a look at fabled Fenway Park.
"I went into that stadium yesterday, and I got back and I actually told my parents, I was like, 'Man, just walking in there, you can feel the history,'" Penny said. "Even the fans around the city, I'm really excited. I walked around there and it was a different feeling."