This season, Baltimore has placed two other outside linebackers on injured reserve ( Vince Biegel and Daelin Hayes) and lost Jaylon Ferguson, who died in June. Tyus Bowser, a starting outside linebacker last year, is on the physically unable to perform list and could return in a couple of weeks.
The Ravens' pass rush struggled in Sunday's 42-38 loss to the Miami Dolphins, which featured the biggest fourth-quarter collapse in team history. Baltimore has four sacks in two games this season.
The addition of Pierre-Paul comes after his second meeting with Baltimore. He visited the Ravens in June, and he left without a deal.
Many of the Ravens players were unaware of the news coming off the practice field.
"Oh s---, he'll give us a lot of pressures. A lot of sacks," Oweh said. "That's good for us."
Ravens defensive coordinator Mike Macdonald deferred questions about the signing of Pierre-Paul to general manager Eric DeCosta but said, "Obviously, JPP's had a great career. He's a heck of a player."
Pierre-Paul, 33, had 2.5 sacks in his fourth and final season with Tampa Bay during which he was hampered by a torn rotator cuff. He underwent shoulder surgery in February and was not re-signed by the Buccaneers in free agency.
When healthy in 2020, Pierre-Paul played a key role in the Bucs' championship run, registering a team-leading 9.5 sacks in the regular season and two in the NFC Championship Game.
A three-time Pro Bowl player, Pierre-Paul has totaled 91.5 sacks in 12 seasons.
ESPN's Jenna Laine contributed to this report.