The O's were relegated to the National League from Sky Bet League Two last season.
Davis was relieved of his duties at Gresty Road in January 2017 following a 3-0 defeat at Mansfield Town, with the Crewe hovering dangerously above the drop zone.
He took Crewe to Wembley in his first season as manager in 2011/12, winning promotion from League Two in the play-off final against Cheltenham Town after ending the season with a sixteen-game unbeaten run to make seventh place and the final play-off spot.
A year later, he guided the club to a comfortable thirteenth place finish in League One, but returned to Crewe a Wembley winner again after leading Alex to Johnstone`s Paint Trophy glory with a final victory over Southend United in April 2013.
Helping Crewe stave off relegation from League One on the final game of the season in both 2013/14 and 2014/15, it wasn't a case of third time lucky in 2015/16 as Crewe were relegated at the bottom of the table.
After a promising start to last season in League Two - leading the club into the automatic promotion spots by mid-September - an alarming run of results led to a slide down the table before the decision was made to part company just days into 2017.
Davis took charge for a total of 272 matches during his five-year tenure as Crewe manager.
Davis is no stranger to the non-League game, the former Crewe, Burnley and Barnsley defender having managed Northwich Victoria and Nantwich Town before his tenure as boss of Crewe.
The 51-year-old will work alongside assistant coach Ross Embleton as they bid for an immediate return to the Football League.