Morrison Utility Services has secured a contract worth up to £750 million to work on the electrical distribution network in the east of England for up to 15 years.
The firm will provide fault management, network enhancement and connection services in the region for UK Power Networks.
MUS has also retained its contract for refurbishing and building grid and primary substations for UK Power Networks, worth £100m over the next five years.
The two deals have boosted its order book to £1.55 billion - or £3.5bn with contract extensions.
MUS chief executive Charles Morrison said: “In the current economy, a growing order book provides us with real opportunities to invest in the future of the business.
“It is essential we continue to develop our people and our systems to ensure we can be innovative and respond positively to our clients’ needs driving year-on-year efficiencies.”