The Latics have failed to score in their last five matches across all competitions and are without a win in their last 10 outings in League One, leaving them bottom of the table and three points from safety.
Tuesday's EFL Trophy defeat to Mansfield Town proved to be Robinson's final match in charge of the team, with Sheridan returning to the club for a fifth spell as either temporary or permanent manager.
"This is obviously a difficult decision. Stephen is a talented coach who we believed could make the transition into a successful manager," chairman Simon Corney told the club's official website.
"Unfortunately things have not worked out for him or the club and we felt that a change needed to be made. I'd like to thank Stephen for the hard work and commitment he has shown and wish him well for the future.
"John is obviously someone we know well and we hope he can have an immediate effect on our current situation."
Sheridan, who was sacked by League Two strugglers Notts County earlier this month, finished his playing career at Oldham before going on to enjoy numerous stints in charge of the club.
The first match of Sheridan's latest spell at the helm will come on Saturday when they host Gillingham at Boundary Park.