Northeast joined Hampshire from Kent, where he was club captain, in 2018, and extended his deal at the club in March this year.
That contract was due to run until the end of the 2022 season, but the player and club have decided to go their separate ways with immediate effect.
Northeast, 31, has enjoyed success at Hampshire, scoring an unbeaten 75 in the 2018 Royal London One-Day Cup final victory over Kent, his former county.
He scored six first-class hundreds for Hampshire, averaging 37, regularly stood in for James Vince as captain, and received call-ups for England Lions while at the county. A full England call eluded him, however.
Northeast has not played for Hampshire since the first Vitality Blast game of the season four weeks ago, and has now left the county.
It is understood that Northeast will join Yorkshire this month on a short-term deal that will take in two vital County Championship matches. After eight matches, they sit second in Group 3 of the Championship, with the top two teams advancing to Division One later this summer.
They face third-placed Northamptonshire from Sunday, and first-placed Lancashire in the Roses match seven days later at Headingley.
After that, Northeast is a free agent. With 25 first-class centuries (plus five more in the white-ball formats) to his name, he is likely to be sought after.