Under the £248 million deal, the construction giant will be providing plain line rail, switches and crossings at a number of junctions, alongside signalling, drainage and electrification operations.
The agreement is a four-year extension to an existing arrangement between the two companies and chief executive Ian Tyler said he and his organisation are "delighted" to be working on the projects.
He said: "These further contract awards demonstrate the strength of our partnership and we look forward to delivering a first-class service to Network Rail."
According to Balfour Beatty, the services will cover all of Network Rail's south-east territory - including Wessex, Sussex, Kent and Anglia - as well as a £27 million initiative for modifications to Glasgow's Paisley corridor.
The firm recently won a £65 million deal for the regeneration of a state in Kensington.