TalkTalk has agreed the £200m sale of its FibreNation fibre network business to CityFibre, a company backed by Goldman Sachs.
The sale of the business had been delayed last year when the Labour Party said it would nationalise BT's Openreach network if it won the general election.
However, the removal of that potential scenario cleared the way for the deal to go through.
TalkTalk chief executive Tristia Harrison said the deal was "good news for TalkTalk, and good news for Britain and its full fibre roll-out ambition".
"Our investment over the last five years and the excellent work delivered by the FibreNation team, combined with CityFibre's well-established platform, will support wide geographic reach of full fibre and further drive competition in the market."