The project is funded by Blaenau Gwent Council and supported by a loan from the Welsh Government.
Work includes the laying of a new track between Ebbw Vale Town and Newport, and the installation of new platforms at Llanhilleth and Newbridge.
Furthermore, it includes a £17m signalling upgrade at the southern end of the line and the installation of a signalling system that will be controlled from the Wales Route Operating Centre in Cardiff.
Network Rail plans to set up site compounds at various locations alongside the railway. These will be used to access the track during the upgrade work, which is expected to take around 18 months.
Network Rail Wales & Borders route director Bill Kelly said that work is now beginning on the Ebbw Vale line that will allow more trains to run in the future.
“A more frequent service will mean passengers between Ebbw Vale Town and Crosskeys will be able to access more jobs, training, and leisure opportunities.”
Between 15 and 18 April, Network Rail plans to undertake a major track upgrade in the Llanhilleth area.
Transport for Wales CEO James Price said: “Transport for Wales will be able to run additional services, and more frequent services when the work is complete as part of our wider programme to transform the Wales and Borders network.
“While the work is taking place we advise passengers to check our new website, our recently-updated app or the TfW social media channels for the latest travel information.”