Mr Miliband said public ownership of Neso would help “build a network that is fit for the future”.
He added: “The new National Energy System Operator has a huge role to play in delivering our mission to make Britain a clean energy superpower.
“We need to move Britain off expensive, insecure fossil fuel markets, and onto clean, cheap homegrown power that we control. This is how we reduce bills in the long term, strengthen our energy independence and support skilled jobs across the country.”
Neso will become part of a web of new organisations overseeing UK energy planning, including GB Energy and a so-called Mission Control unit.
All three will work with Great British Nuclear, another new body within the Energy Department responsible for driving the delivery of new nuclear projects.
A government spokesman said: “Currently, there is no single body responsible for overseeing the strategic planning and design of the country’s electricity and gas networks.
“Neso will fill this gap – breaking down the silos which currently exist between the planning of electricity and gas systems, with independent oversight for the design of all Great Britain’s energy networks.
“The move will enable investors to build out new energy infrastructure with confidence in how their project will fit into the country’s wider clean energy plan.”
Neso has been established through powers under the Energy Act 2023, making it responsible for maintaining UK energy supplies, protecting consumers and planning a future low-carbon energy system.
This means it covers not just electricity and gas but also hydrogen, renewable generation, energy storage and emerging technologies like carbon capture and storage.
Mr Slye said: “We are excited to optimise our national approach to energy.”
A spokesman for the Energy Department added: “Whilst the Energy Secretary will be the sole shareholder of Neso, we are deliberately setting Neso up to be operationally independent of government.”