Adams apparently made his decision following talks with chairman Norman Smurthwaite on Thursday morning.
Vale have lost their last six games on the trot and Adams admitted after Tuesday night's home defeat to Bristol City that he didn't know if his shelf life at Port Vale was up.
Adams said today: "It is with great sadness that I have decided to leave Port Vale but I believe I am leaving the club in a stronger position than when I joined.
"I have spent five years in Burslem, punctuated by a spell at Sheffield United, and although the role of a football manager brings with it a roller-coaster of emotions, I will never forget my time at Vale and the many happy memories I will take away with me.
“This has not been an easy decision to make, which has been made even more difficult by the strong relationships I have forged during my time at the club. I would like to thank my immediate team, all of the staff at Vale Park and the many players I have worked with throughout my two spells. I have met some truly fantastic people.
“In addition, I would like to thank all of the Port Vale fans for their fantastic support. I hope that the club has only bright times ahead.
“I believe now is the time for another manager to take the helm and I would like to thank Norman Smurthwaite and his wife Lorraine for their fantastic support. I wish the club every success for this season and the future.”
Chairman Norman Smurthwaite added: “During his time at the club, Micky helped Port Vale to deliver a positive period in the club’s history, including promotion to League One, against a backdrop of instability.
“Although I was not involved with the club when Micky joined five years ago, I don’t think anyone should underestimate the contribution he has made, to both on and off-field matters. He has been a fantastic figurehead for Port Vale who has helped the club get positive national recognition once again.
“Throughout the time I have known him, he has led the club with great passion and professionalism and it’s with a heavy heart that I accept his resignation today'
“On behalf of everyone at Port Vale, I would like to thank him for his contribution and I wish him nothing but good fortune for the future.”
Adams will not be out of work for long though given his track record, with Vale the fourth different club he has won promotion with. Former Watford and Sheffield United stalwart Rob Page, who has been assistant manager and head coach looks set to take the reigns at Vale Park for now whilst the Chairman decides what course of action to follow.
Vale face another relegated side in Barnsley on Saturday.