The 18-year old has been a regular in the reserves and youth team over the last two seasons and he spent time on loan at Cammell Laird in 2009-10.
Mackreth has been with Tranmere since the age of 13 and has just completed his two-year scholarship at Prenton Park.
Rovers boss Les Parry said: "Jack is a promising young winger who I'm pleased will be in the first team squad next season.
"He's very fast, good on the ball with both feet and hard working.
"This is a big opportunity for Jack and if he continues to work hard I'm sure the chance to impress the fans will come his way."