Morrison Utility Services' contract is worth around £70 million a year and the contract with Enterprise Managed Services is valued at up to £50 million a year.
The former will carry out work in the East Midlands, East Anglia and North London, while the latter will operate in the West Midlands and the North West.
"National Grid is committed to providing the most efficient and effective service to all of its customers, and these new partnerships in gas distribution will ensure we continue to work to those high standards," National Grid executive director Mark Fairbairn said.
Meanwhile, National Grid's American arm is hoping to get hold of US$100 million (£67 million) of funding from Barack Obama for green energy projects.
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