Roddick earned his fifth title in a Masters 1000 tournament — one level below the Grand Slams — and his first since 2006.
He coaxed an errant backhand from Berdych on championship point, and responded to the crowd's cheers with a thumbs-up. The runner-up last month at Indian Wells, Roddick has a record of 26-4 this year, best on the men's tour.
"The last month has been real good for me," he said. "I've played well on the big moments. I've been able to have a game plan and execute it, regardless of what kind of shots it takes. So it's all good. It's all encouraging."
The title was Roddick's second at Key Biscayne, where he also won in 2004.
Seeded sixth, he varied the pace on his groundstrokes to keep Berdych off balance while committing only 16 unforced errors. He had 13 aces and never faced a break point.
Roddick lost only seven points on his serve in the second set and dropped just two service games in the tournament. But he also showed that at age 27, he can rely on more than just a big serve.
"A lot of people say the serve is fine and the rest of it's pretty average," he said. "That's all right. But there are a lot of guys with big serves who are pretty average, so there's got to be some difference."
Roddick's slice backhand repeatedly forced the 6-foot-5 Berdych to hit the ball at ankle level, robbing his forehand of power. While searching to find a rhythm with his strokes, Berdych also lost track of the score in the ninth game, lining up to serve from the wrong side.
The match turned two games later, when Roddick reached break point for the first time. He broke when Berdych hit a forehand out, then held at love to take the first set.
That was part of a streak where Roddick won five consecutive games. He broke again to start the second set when Berdych hit another errant forehand.
The No. 16-seeded Berdych, playing in only his second Masters 1000 final, made just 48 percent of his first serves. He reached deuce on Roddick's serve only once.
Roddick varied the pace of his serve, which topped out at 136 mph.
"He was just too strong today," Berdych said. "He's not just serving the big bombs. His variations of the serve are a really big improvement. ... I was really looking for maybe to get one chance, but he held pretty well. I didn't get any chance during whole match."
Since hiring Larry Stefanki as his coach in late 2008, Roddick has lost at least 10 pounds, improved his foot speed and developed a more well-rounded game, which has allowed him to win with a variety of tactics.
"He works as hard or harder than anybody else on this tour," Stefanki said. "He could be similar to Andre Agassi, where his best years are from 27 on."
In the semifinals, Roddick reached the net often to beat Rafael Nadal. But volleys weren't much of a factor in the final, with Roddick winning only eight of 16 points at the net, and he instead took control from the backcourt.
Roddick earned $605,500. Berdych, who beat top-ranked Roger Federer in the fourth round, received $295,500.