The deal is worth $9.5 million, a source confirmed to ESPNNewYork.com.
Visnovsky was believed to be a trade target for teams looking to bolster their blue line, but with the Islanders challenging for a playoff spot general manager Garth Snow decided to lock him up.
The 36-year-old, who has three goals and six assists in 22 games for the Islanders this season, was set to become an unrestricted free agent this July. Before inking an extension with the Isles, Visnovsky was on the last year of a five-year, $28 million deal.
Visnovsky's tenure with the Islanders has been an interesting one. After being acquired by the Islanders in a trade with Anaheim last summer, Visnovsky tried to void the deal. Visnovsky filed a grievance with the NHL Players' Association that his no-trade clause, waived in his trade from Edmonton from Anaheim in 2010, was not honored.
An arbitrator ultimately ruled against him, but Visnovsky refused to report to the Islanders once the lockout ended and was subsequently suspended by the team. The Topolcany, Slovakia, native appealed to remain in the Kontinental Hockey League, citing "personal reasons," although that request that was denied.
Since joining the Islanders, Visnovsky's addition has bolstered the team's blue line. Visnovsky joined veteran captain Mark Streit as leaders of the team's back end. The Islanders are also attempting to re-sign Streit, multiple sources have confirmed to ESPNNewYork.com.
Both Streit and Visnovsky are believed to have garnered interest with the NHL's trade deadline approaching, but Snow is now in a different position as previous years.
With a 4-3 win over the Flyers on Thursday night, the Islanders matched the Rangers' 35 points, though the Rangers have a game in hand.
Riding a three-game winning streak, the Islanders are in sole possession of ninth place in the Eastern Conference standings. They have missed the playoffs the past five seasons.
Information from The Associated Press was used in this report.