The settlement between EDF Energy, West Somerset, Sedgemoor District and Somerset County Councils, comes after months of discussions between the parties on how to mitigate the impact of the new nuclear reactor.
The signing of the deal comes after Utility Week revealed last month the councils had agreed the wording of the section 106 document.
Under the agreement, EDF will invest more than £64million on supporting local communities and services such as education, training, transport and housing. Earlier in the year EDF Energy committed £30million to early site preparation works.
The mitigation package is subject to planning consent and a final investment decision on the Hinkley Point C project, due at the end of the year.