The pair will not be offered new contracts when their current deals expire.
Oliver, 23, scored three league goals in 16 league starts for the Railwaymen after signing from Lincoln in the summer of 2013. The striker’s most notable goal saw him net the winner against neighbours Port Vale in September.
The former Sheffield Wednesday trainee spent the majority of this season on loan at Mansfield, where he scored seven league goals in his 23 starts to help the Stags remain in the Football League.
Central defender Stewart joined Crewe on a six-month contract in November from Wycombe. The 22-year-old made 10 appearances for Alex.
Manager Steve Davis told the club’s official website: “It is always tough to make decisions on players and I believe it is the right decision to let this players move on and try and establish themselves in a team somewhere.
“At the age that they are they should be playing more regularly. It is important for their development and it is a career decision.
“They probably don’t think that at the moment but later on they will hopefully look back and think it was the best thing for progressing their career.”