Born in Swaziland, Easter is comfortable in all three back-row positions and will link up with his new team mates at Edgeley Park this summer.
"This is another good signing for the club. I have watched Mark's progress at Northampton and am very impressed with him. He hasn't had the starts he wanted at Franklins Gardens and was looking for a new start. He is an ambitious young man with a great work ethic and will fit in well when he joins us at the end of the season," said executive director of rugby Steve Diamond.
Mark Easter said, "I feel that the opportunity and challenge presented by Sale Sharks is the right move for me at this stage of my career. The squad being built by Steve Diamond shows ambition and a clear direction - which I want to be part of. I also want to thank Northampton Saints and the fans wholeheartedly for the past five years and I wish the club all the best for the future".