Major construction was planned to begin in early 2021 but was delayed to April 2022 after Alberta's United Conservative provincial government failed to contribute the province's pledged portion of the line's funding.

[10][11][12] This came after months of speculation from city officials, politicians, and journalists that the provincial government and others associated with the United Conservative Party[13][14][15][16] were attempting to stifle or cancel the Green Line.

[17] Due to the provincial government's actions, the City of Calgary temporarily paused the project's procurement though planning, pre-construction and public engagement continued through 2021.

[12] Delays persisted until the project received final approval from Alberta's provincial government on July 7, 2021,[18] hours after Prime Minister Justin Trudeau met privately with Jason Kenney in Calgary.

This meant the project had full approval from all three orders of government and Prime Minister Justin Trudeau stated "The money is there and the agreements are signed, so regardless of an election, the Green Line is going to go forward.

[25][26] The full vision of the line will run from north-central to southeast Calgary on 46 kilometres (29 mi) of track and will feature 29 stations.

These were:[33] When completed, Stage 1 of the Green Line will feature: When the full line is complete, it will also feature 12 bridges, 10 park and ride facilities (with 5,000 to 6,000 parking stalls), 10 tunnels (including the 2 km (1.2 mi)-long centre city tunnel from 2 St SW in Eau Claire to 11 Av SE in Victoria Park), a bridge connecting Eau Claire to Centre Street North, and 2 LRV maintenance and storage facilities (at Shepard and 96 Avenue N).

[40] The Green Line will restore the historic alignment of Calgary's trams, running trains on the surface of Centre Street as well.

[41] As early as 1986, the communities of McKenzie Towne, New Brighton and Copperfield had set aside land along 52 Street SE for the future line.

[43] Chronic congestion on Deerfoot Trail is partly attributed to the failure to construct the Green Line before the 1.25 million population target.

[47] In May 2017, the city revealed the line's suggested alignment and announced it would be built in stages due to the unexpectedly high costs of certain design choices.

The revised alignment replaced the deep-earth tunnel under the Bow River with an elevated guideway over the east end of Prince's Island Park.

[56] As the project's approval was looming in early 2020, a group of business people, some with ties to the United Conservative Party,[13] organized an invite only event at the Calgary Petroleum Club with city officials.

[60] One of the participants, oil industry executive and multimillionare Jim Gray, suggested the group was not opposed to the line but instead wanted to "de-risk" it.

[60] The group called for replacing half of the rail line with a bus, cancelling the downtown subway, and for the use of high-floor trains.

The group has been noted for disseminating disinformation about the project and has made objectively incorrect claims in an attempt to garner opposition, such as the unfounded assertion that property taxes could increase by 90 percent if built.

[61] The group also published editorials in local newspapers, like the Calgary Herald, making a variety of dubious claims about the project and calling for its pause or cancellation.

[64] Despite the issue cited as the reason the province failed to contribute their pledged portion of the project's funding being resolved, the United Conservative provincial government then announced that it would continue withholding funding, the city needed to produce a new business case for the line, and it would be investing in the widening of Deerfoot Trail.

[66][10] On July 7, 2021, Prime Minister Justin Trudeau met privately with then-Alberta Premier Jason Kenney at the Fairmount Palliser Hotel in downtown Calgary.

[18] After over a year of delays inflicted by the provincial government, Prime Minister Justin Trudeau, Mayor Naheed Nenshi, members of council, and various other stakeholders gathered at the Oliver Bowen Light Rail Maintenance Facility in Calgary to announce the Green Line would continue as planned.

[68] On June 16, 2020, council voted 14 to 1 to approve construction Stage 1 of the Green Line despite vocal opposition from a small group of wealthy and influential businesspeople.

[69][70] On July 10, 2021, Prime Minister Justin Trudeau said "The money is there and the agreements are signed, so regardless of an election, the Green Line is going to go forward.

"[19] The City of Calgary began early works construction in 2017 with utility relocation and environmental redemption projects along the alignment of the line and spent over $500 million.

[71] In November 2021, Construcciones y Auxiliar de Ferrocarriles (CAF) was awarded the contract to supply Green Line's new fleet of low floor trains.

[72] A month later, Calgary and the provincial government agreed to build the southeast section of Green Line and revive five cancelled stops.