Wartsila monitors the plants in real time using its condition-based maintenance services to evaluate their performance and ensure efficient operations.
The company will also train local staff so they can better operate and maintain the plants.
The plants service both the residential and commercial market, and infrastructure like ports and airports.
Hera, close to capital Dili, has an output of 119 megawatts and has been in operation since the end of 2011.
Betano has been operating since May 2014 with an output of 134MW.
"This operation, maintenance and training contract with Wärtsilä will help us to ensure stable electricity supply in Timor-Leste," Electricidade De Timor-Leste director general Virgilio Guterre said.
Wartsila Indonesia president director Erwin Vanderkerff said the government could now focus on the future development of the power supply infrastructure of the country.
Timor-Leste has been working to secure its energy in recent years and in late August finally came to diplomatic accommodation with Australia for a maritime boundary between them in the Timor Sea which will facilitate the development of Woodside Petroleum's Greater Sunrise field.
Timor-Leste has also handed out the first onshore exploration contract since independence, to Australian entity, Nepean's Timor Resources.
Though still considered a "least developed" country by the United Nations the small former Portuguese and Indonesian colony has been working to improve its infrastructure in recent years.