The money will be ring-fenced within the next round of the Contracts for Difference (CfD) allocation, due to open next month, and will be used to help providers lower their costs in the development of their technologies.
“With this investment, Wales can continue to develop its potential as a leader in renewable technology and industry and contribute to the greener global economy of the future,” said Welsh Secretary Simon Hart.
A private sector consortium previously tried to get a tidal lagoon off the ground in Swansea, but the project stalled amid concerns over the level of risk, cost of energy and public sector refusals to underwrite the initiative.
However, a new consortium has recently put plans forward for a newly-formed tidal lagoon at Swansea, known as Blue Eden Lagoon.
In May the Welsh government said it had received a “strong response” to its Tidal Lagoon Challenge plans, which sought interest in the concept of tidal power along the Welsh coastline.