The right wing, who spent all four of his NHL seasons with the Montreal Canadiens, signed a US$12-million, three-year deal with the team that scored the sixth fewest goals last season.
"He has a terrific shot, very strong on the puck and plays a gritty game," Bruins general manager Peter Chiarelli said on a conference call. "He's someone we've targeted for a while."
Ryder was the second forward on Chiarelli's list of free agents. The Bruins also were interested in Marian Hossa, who finished last season with Pittsburgh and has scored at least 29 goals in eight of his 10 seasons.
"We were involved a little bit with Hossa," Chiarelli said. "He's a terrific player. We weren't at a position where we felt we would devote time to it."
At least two other teams were trying to sign Ryder, Chiarelli said, and the Bruins increased their offer at about 7 p.m. ET, three hours before the deal was announced.
"You get to the point and you sense maybe we're not going to get this guy," Chiarelli said, "but you can't stray too much from it. There was a lot of waiting. We had a lot of repeat discussions" among Ryder and club officials."
Chiarelli said he doesn't expect to sign other free agents.
After scoring 30 goals for two straight seasons, Ryder had just 14 last season with 17 assists. He played in four of the Canadiens first five playoff games in Montreal's seven-game, first-round victory over Boston. But he didn't dress for the team's remaining seven.
"He was in the dog house," Chiarelli said. "I don't know the facts behind it. I don't know what to attribute it to. They had some very skilled players. Every time we played him he played hard and he was dangerous."
The Bruins defense was solid last season, their first under Julien. But they scored just 212 goals.
In 314 career games, Ryder has 99 goals - 46 on the power play - and 108 assists.
The Bruins reached the playoffs last season one year after posting the third worst record in the Eastern Conference. But they still haven't won a playoff series since 1999, when they beat Carolina, and have been in the playoffs in just four of the last eight seasons.
Their best offensive player, Patrice Bergeron, played only 10 games before a concussion ended his season in October. Philadelphia defenseman Randy Jones knocked him unconscious with a hit from behind that smashed his face into the glass.
Just 22, Bergeron scored more than 20 goals in each of the previous two seasons.
"You can't forget that Patrice Bergeron is coming back," Chiarelli said. "If this is the team that we go into training camp with I'd be happy."