The defensive lineman passed his conditioning test Sunday morning, clearing the way for him to join practice, a source told ESPN NFL Insider Adam Schefter.
Haynesworth, who wore No. 92 during the team's morning walkthrough at the team's training facility at Gillette Stadium, stole the show.
Upon arriving on the practice fields, Haynesworth was greeted with and acknowledged cheers from the capacity crowd. During the first 11-on-11 work of the session, Haynesworth lined up along Vince Wilfork on the inside of a four-man line and wowed the crowd by mauling through guard Rich Ohrnberger and center Ryan Wendell to crash the backfield.
However, Haynesworth had little if any participation in the remaining drills of practice, and was seen doing stretching work with the team's training staff instead of running end-of-practice sprints. While clearly a dominating force when in action, Haynesworth's health is something that bears watching.
The Patriots officially announced the acquisition of Haynesworth on Friday, and when Haynesworth didn't practice Saturday, it prompted speculation that he didn't pass the team's conditioning test. Haynesworth, of course, had famously repeatedly failed conditioning tests during his rocky tenure with the Washington Redskins.
That speculation was fueled in part by coach Bill Belichick's non-answer to a question about the defensive lineman. Asked if Haynesworth had passed his conditioning test, Belichick said, "There are things we still need to do with Albert for him to be able to get on the practice field, and when those things are done, he'll be out there."
How Haynesworth fits into the Patriots' defense will be a top story line in training camp.
"With any player, you're trying to identify their strengths and their weaknesses, what they do well. The reality is that any player we bring into this program, they're going to define what their role is going to be with their performance and what they do on the field," Patriots director of player development Nick Caserio said Sunday. "The more they can do, and they can execute those assignments and techniques, then they'll be put in that position.
"Albert has been a good football player in this league. He's big, he's strong, he's athletic, he's a disruptive player. I think we've all taken the approach that if the guy is a good football player, we'll find a way to use him, and in the end it's up to the player to determine what his role is going to be moving forward."
Mike Reiss covers the Patriots for ESPNBoston.com. Information from ESPNBoston.com's Mike Rodak was used in this report.