The section between Atwater and Frontenac was part of the initial network; the line was extended to Honoré-Beaugrand in 1976 to provide easy access to 1976 Summer Olympics sites.

On November 3, 1961, Montreal City Council approved an initial Metro network 16 kilometres (9.9 mi) in length.

Construction of the first two lines began May 23, 1962,[3] under the supervision of the Director of Public Works, Lucien L'Allier.

On December 20, 1967, Frédéric Back completed his art piece L'histoire de la musique à Montréal (The history of music in Montreal) in Place-des-Arts station.

The opening of the section between Frontenac and Honoré-Beaugrand took place on June 6, 1976,[6] six weeks before the start of the Summer Olympics.

[7] In 2024, following years of studies, the STM's parent agency, the ARTM, in conjunction with the Ministère des Transports et de la Mobilité Durable du Québec and the City of Montreal began conducting surveys regarding a possible extension of the Green Line westwards towards Lachine.

[11] The STM also noted that to increase the capacity of the Green Line by 37%, works to upgrade garages and signalling systems would also be required.