The contract has an average annual value of $3 million.
DeMelo was acquired by the Jets before this year's trade deadline from the Ottawa Senators. He recorded 10 assists and 37 penalty minutes in 59 regular season games with the Jets and Senators during the 2019-20 campaign.
The 27-year-old played in all four post-season games against the Calgary Flames, leading the Jets in shorthanded ice time with 16:11.
The London, Ont., native was drafted by the San Jose Sharks in the sixth round of the 2011 NHL Draft, 179th overall.