Borowiecki, 25, is entering the final season of his contract and could have become a restricted free agent had he been unsigned after the 2014-15 season.
"Obviously there's still no guarantees," Borowiecki told the Ottawa Sun. "It is a bit of security and confidence, but at the same time it's a bit of a kick in the pants, too. I'm 25 years old, it's time for me to sort of cement myself as a full time NHLer. This gives me the chance to do it."
The contract will start with the 2015-16 season; he'll receive $1 million that season, $1.1 million in 2016-17 and $1.2 million in 2017-18, for an average annual value of $1.1 million.
An Ottawa native, Borowiecki had one goal and 48 penalty minutes in 13 games for the Senators last season. He had two goals, six assists and 158 penalty minutes in 50 games for the Binghamton Senators in the American Hockey League.
"I think for me it's bringing jam and energy," Borowiecki told the newspaper. "I've always been an up-tempo player, maybe sometimes a little too up-tempo, but I play hard, I play physical.
"I think down in the AHL I showed I was a pretty steady, reliable player. Now it's time for me to do that here."
Borowiecki (6-foot-2, 205 pounds) has one goal and 68 penalty minutes in 21 games, all with Ottawa. He was selected by the Senators in the fifth round (No. 139) of the 2008 NHL Draft.