It is understood the pair told administrators before last weekend’s defeat at Tranmere Rovers they intended to leave the club and will not be in the dugout for this Saturday’s home clash with Ipswich Town.
Speaking to The Bolton News, Parkinson confirmed he had spoken to the League Manager’s Association and added: “I felt it was the right time to go”.
Jimmy Phillips looks set to be handed the reins part-time as Wanderers begin the search for a new manager.
Goalkeeper coach Lee Butler, fitness coach Nick Allamby and physio Matt Barrass are expected to remain in position until further notice.
Parkinson was the 15th longest-serving manager in the EFL, having served for three years and 70 days since his arrival from Bradford City.
The 51-year-old has taken charge of 156 matches in league and cup, leading Wanderers to promotion from League One in his first season with a last-day victory against Peterborough United despite spending the entire campaign in a transfer embargo.
Parkinson then helped keep the club in the Championship – courtesy of another last-day victory, this time against Nottingham Forest – having not spent a single penny on transfers.
His third full season lurched from one disaster to another as pay problems, player strikes and the disintegration of Ken Anderson’s ownership led to administration in May, by which time the club had been relegated back to the third tier.
Parkinson agreed to stay on and assist the administrators over the summer but again encountered problems as a delay in selling the club forced him to field the youngest-ever Bolton line-up for the 0-0 draw against Coventry City.
The Bolton News has learned that Parkinson and his assistant manager Parkin made up their mind to leave after the takeover failed to materialise on August 8, when Laurence Bassini successfully gained a High Court injunction to stop the deal in its tracks.
Potential new owners Football Ventures did attempt to convince Parkinson and Parkin to stay but with work to be done in the transfer window the pair felt now was the right time to go.
A spokesperson for Bolton Wanderers Football Club said this evening: "The club has received the notice of resignation from manager Phil Parkinson and assistant manager Steve Parkin and the matter is being considered."
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