The National League North title chasers announced he had resigned following Saturday’s 1-0 victory at Chorley.
They said he was leaving “take up an alternative post at another club" - and now we know where.
The former Salisbury, Eastbourne and Hemel Hempstead manager replaces Ross McNeilly, who was given the job in December until the end of the season.
He sacrifices a promotion push to move to the National League club, with second-place Lynn five points behind leaders AFC Fylde.
A Shots statement read: "Ross McNeilly has been relieved of his first-team duties.
"Tommy Widdrington will take charge of first-team affairs from our return to training on Monday.
"We'd like to thank Ross for his hard work and effort and welcome Tommy to the Shots."
King’s Lynn’s search for Widdrington’s replacement has already begun, the club told fans.