The single £200m contract is set to replace about 50 external ones currently in place, by April 2014.
Originally, the council said it was looking to invite five firms to bid but has now extended the tenders list.
Cllr John Bint, cabinet member responsible for transport and highways said: “We can deliver better highways maintenance services at lower cost to Milton Keynes residents by using one carefully chosen contractor than the current arrangements involving some 50 suppliers, all on different contracts.
“This is an important milestone in the process towards better services and better value.”
Bidders must submit tenders by 5 August with the council aiming for a contract award by next January.