The deal is worth up to £750m and involves design, programme management, construction and technical support for National Grid’s electricity network.
Balfour Beatty and National Grid formed the Electricity Alliance East partnership five years ago to secure the long-term stability of much of the UK network.
Work involves the ongoing maintenance and refurbishment of overhead transmission lines, as well as designing and delivering National Grid’s upgrade plans across the network.
Balfour Beatty Chief Executive, Ian Tyler, said: “National Grid is one of our longest held relationships and we are delighted at their decision to extend the long-term partnership with Balfour Beatty.
“This further reinforces a strong, strategic alliance bringing continuing value as well as ongoing certainty to a core element of the UK’s infrastructure.”