Westport said the deal secures its position as Ford's largest partner under the qualified vehicle modifier program.
The company also announced a $5-million joint marketing and sales program that will include purchase incentives for fleets and a commitment from Clean Energy to purchase Westport products.
Clean Energy Fuels manufactures compressed natural gas and liquefied natural gas equipment and has natural gas fuelling stations across North America.
Under the deal, Westport will pay Clean Energy Fuels $25 million in stock based on a share price of $30.62.
Westport shares closed at $34.77 on Thursday.
Westport develops engines that use fuels such as compressed natural gas, liquefied natural gas, hydrogen and renewable natural gas fuels such as landfill gas.