The 18-year-old academy graduate, who can play at full back or in midfield, has been rewarded with a short term deal by boss Darren Ferguson.
“I am over the moon, ever since I was a little boy all I ever wanted was to sign a professional contract and now my dream has come true, it is a great feeling,” Walker told Rovers’ official website.
“Players like Harry Middleton and Liam Mandeville have already been given a chance, so I am going to go away and work hard during pre-season.
“Harry and Liam have given me advice, which is to get your head down in training and work hard, give yourself that chance to impress the manager and you never know what might happen.”
Walker follows in the footsteps of fellow youth team graduates Reece Fielding and Will Longbottom, who both made their first team debuts last season in the Checkatrade Trophy.
“A lot of the younger players in the squad played in the Checkatrade Trophy last season and that is one of my targets, to get some game time in that competition and then ultimately get some League One games,” said Walker.
“I would like to break into the Under 21s side too. I want to play as many games as possible during this six months with the side.
“It is an unreal feeling to be around the first-team set up with the players who are all preparing themselves for the upcoming games and I want to break into the first team squad.”
Walker joined Rovers’ academy in 2008.
Tickets for Rovers’ opening pre-season friendly at Armthorpe Welfare on July 11 (7.30pm) are available from the Keepmoat Stadium priced £5 for adults and £3 concessions.