If you're heading into Leeds from the south, the speed limit on the anti-clockwise carriageway will be reduced to 30mph and lanes will be narrowed.The 24-hour restrictions will last until May while the improvement works are completed.
From February 26, the lowered limit will also be in place on the clockwise carriageway, affecting drivers joining it from the west.
Engineers will be working to install new safety barriers and improve drainage between junctions 3 and 6.
Overnight closures will also be introduced during the 10-week project. The times will be altered during major events such as Leeds United matches.
Highways England's long-term plan for the M621 will see some junctions closed and extra lanes added.