It comes amid growing demand from homeowners, businesses and green energy projects such as wind farms for improvements to the infrastructure.
Scottish Hydro Electric Transmission, part of energy giant SSE, says the work will deliver new or upgraded power lines to areas including Caithness, Fort Augustus and Beauly, and will help support more than 600 jobs as well as local projects.
SSE awarded the contracts to Balfour Beatty, Amec, Babcock and MSVE Transmission, a venture of Morgan Sindall and Vinci Energies.
David Gardner, director of transmission at Scottish Hydro Electric, said: "These contracts, with some of the industry's global experts will help deliver the infrastructure needed to support the connection of renewables, as well as providing a boost to the local communities where we are operating.
"We've made sure that communities, local employment and the local supply chain are at the heart of the contracts. This will build on the work we are already doing to develop a trained, skilled workforce."
In 2012, SSE and the University of the Highlands and Islands signed an agreement aimed at helping Highland communities make the most of the opportunities arising from the energy industry.