The 33-year-old, who is the younger brother of Harlequins number eight Nick, joined Sale in 2011 after six years at Northampton.
Easter won the European Challenge Cup and reached the Champions Cup final at Saints after joining from Nottingham.
"I've enjoyed my time at Sale, I didn't really want to go anywhere else," said the back-row forward.
"It was the right time to leave on my own terms, which not many people do.
"I've had the chance for these last few games just to enjoy and savour them and I've been really lucky."
He will now take up his teaching position at Wrekin College in Shropshire after the final game of the season at Newcastle on Saturday.
"The last few years, I've been tailoring my career towards teaching, so taking a few courses, getting into schools, teaching and coaching," he added.
"The opportunity just came up at the right time. It felt like the right time for me and my family."
Sale Sharks forward Mark Easter has announced he will retire at the end of the season to take up a teaching role.