Marchant was head of SSE for ten years before he stood down in the summer last year.
The Edinburgh-based company has designed, built, and deployed a community owned 30kW tidal turbine in the Bluemull Sound in Shetland.
In June, Nova Innovation received a grant for £3.75 million to help a tidal 500kW tidal array at the same site.
Following Marchant’s appointment, Simon Forrest, managing director of Nova Innovation, said: “Ian’s appointment helps strengthen the Nova board as we continue to grow our business.
“He brings a wealth of experience and insight that will accelerate Nova’s growth and commercial development.”
Marchant added: “I am extremely impressed with the team’s focus on the commercial realities of tidal energy, their commitment to design and manufacture here in Scotland, the importance of community involvement in their activities and the clear values that drive the business.
“I believe that tidal energy production can make a meaningful contribution to the production of clean affordable energy and believe that Nova have the right strategy to make this happen.”