The offshore Southeast Gateway Pipeline will supply natural gas to Mexico's central and southeast regions, the Canadian pipeline operator added.
The deal with Comisión Federal de Electricidad (CFE) comes as Canada and the United States are having their most serious trade spat with Mexico over the United States-Mexico-Canada Agreement.
TC Energy said sanctioning of the pipeline would expand its secured capital program to $33 billion and could add to its 2021-2026 adjusted EBITDA growth outlook.
Last month, TC Energy had said it would build a $5 billion gas pipeline with CFE in the Mexican state of Veracruz.
(Reporting by Ruhi Soni in Bengaluru)