The signing came less than two days before the start of the NFL free agency period.
"I was confident all along that this was going to get done I didn't panic one bit," Jacobs said in a statement released by the team. "I know the reason we did it the way we did; I knew I was going to be here. I was super-confident and I am here. I'm happy about it."
The deal includes $13 million in guarantees. Jacobs will earn $15 over the first two years.
Putting a franchise tag on Jacobs earlier this month guaranteed him a $6.6 million salary next season.
The 264-pound mainstay of the Giants' running attack the past two seasons, Jacobs signed the deal on Wednesday after the two sides hammered out the agreement over the past week.
"This team is full of young talent," he said. "We brought some great talent in here the last two years and those guys are still learning and getting better. Our offensive line is great and will continue to be great. There are a lot of young guys on our team that are still playing great, great football. I'm looking for big things out of our football team next year."
Despite missing three games with a knee injury, Jacobs ran for 1,089 yards and a team-leading 15 touchdowns in helping the Giants win the NFC East last season. He also combined with fellow halfback Derrick Ward (1,025 yards) to make the Giants only the fifth team with two 1,000-yard running backs.
Ward also became a free agent after this past season.
"Both parties are happy to get a long-term deal done," general manager Jerry Reese said. "Now Brandon can totally concentrate on the offseason program and get himself ready to go this fall."
If Jacobs he had remained a free agent, the Giants could have matched any offer made by another team or allow him to sign with that team in exchange for two first-round draft picks.
Jacobs has rushed for at least 1,000 yards in each of the past two seasons, joining Joe Morris (1985-86), Rodney Hampton (1991-95) and Tiki Barber (2002-2006) as the team's only backs to have consecutive 1,000-yard seasons.