The main predecessors of the TTC were: In 1861, the City of Toronto issued a thirty-year transit franchise (Resolution 14, By-law 353) for a horse-drawn street railway, after the Williams Omnibus Bus Line had become heavily loaded.

In 1923, the TTC took over the Lambton, Davenport and Weston routes of the Toronto Suburban Railway (TSR) and integrated them into the streetcar system.

After the Second World War, many cities across North America and Europe[9] began to eliminate their streetcar systems in favour of buses.

It also continued to rebuild and maintain the existing fleet of PCC (Presidents' Conference Committee) streetcars until they were no longer roadworthy.

However, as that line was being built, the Province of Ontario persuaded the TTC to switch to using a new technology called the Intermediate Capacity Transit System (now Bombardier Innovia Metro) by promising to pay for any cost overruns (which eventually amounted to over $100 million).

The first new line was route 604 Harbourfront, starting from Union station, travelling underneath Bay Street and rising to a dedicated centre median on Queen's Quay (along the edge of Lake Ontario) to the foot of Spadina Avenue.

The new tracks are expected to last 25 years after which only the top concrete layer needs to be removed in order to replace worn rails.

[17][18] Route 512 St. Clair was rebuilt to restore a separated right-of-way similar to that of the 510 on Spadina Avenue, to increase service reliability and was completed on June 30, 2010.

[24] On November 22, 2015, the TTC started to operate its new fleet of Flexity Outlook streetcars from its new Leslie Barns maintenance and storage facility.

[26] At the same time, the TTC also activated the option for customers to purchase single-ride tickets using debit or credit cards on the fare vending machines on Flexity streetcars.

[28] The eastern end of the 514 route ran on a newly constructed branch, originally named the Cherry Street streetcar line, which is located in a reserved side-of-street right-of-way.

[33] That December, the TTC eliminated the option for passengers to purchase single-ride tickets by credit and debit cards on the Flexity streetcars due to reliability issues with the fare vending machines.

[35] The next day, due to the construction work at the Queen, Kingston Road, Eastern Avenue intersection, the TTC eliminated the 502 Downtowner service indefinitely.

On August 15, 2023, the credit and debit card single-ride fare payment option was reintroduced as part of a system-wide TTC rollout.

Part of the Blue Night Network service, operating as 301 Queen between Neville Park and Long Branch Loops.

However, newer trackage has largely been established within dedicated rights-of-way to allow streetcars to operate with fewer disruptions due to delays caused by automobile traffic.

Short sections of the track also operate in a tunnel (to connect with Spadina, Union, and St. Clair West subway stations).

The most significant section of underground streetcar trackage is a tunnel underneath Bay Street connecting Queens Quay with Union station; this section, which is approximately 700 m (2,300 ft) long, includes one intermediate underground station at Bay Street and Queens Quay.

Streetcar track and overhead power line were also installed at the Fleet loop, which is located at the Queen's Wharf Lighthouse.

[64] In 2019, the City of Toronto approved new track linking Dufferin Gate and Exhibition Loops; however, as of 2022[update], no construction has started.

[85] By June 2020, the streetcar shortage had been alleviated by the reduction in ridership due to the COVID-19 pandemic in conjunction with temporary bus replacements on routes 511 Bathurst and 506 Carlton to accommodate construction projects.

[94][95][96] On October 22, 2020, the TTC board approved the immediate purchase of 13 additional streetcars from Bombardier for delivery in 2023, with an option for 47 more cars, if funding from senior levels of government became available.

[a] Because of failing electronics, defective antennae, or the failure of the system to unlock after passage of a car, there is the risk of a streetcar taking the wrong path at a switch.

[109] Since all of Toronto's current streetcars are single-ended, turning loops are provided at the normal endpoints of each route and at likely intermediate turnback locations.

[119] With pantograph operation, the TTC expects Flexity streetcars to have more efficient heating and air conditioning systems, better vehicle performance and fewer delays caused by disconnections from overhead wires.

[121] During a rainy period in February 2018, the TTC received an incentive to expedite the conversion of the electrical overhead for pantograph use by the Flexity streetcars.

It is located in the tunnel under Bay Street, shared by the 509 Harbourfront and 510 Spadina routes, between Queens Quay West and Union subway station.

By creating a smaller service area, it is easier for TTC crews to keep track and overhead wires free of snow and ice.

In the event of a severe storm, the TTC replaces streetcars with buses on routes 506 Carlton, 511 Bathurst, and 512 St. Clair, plus the outer portions of 501 Queen and 504 King.

[137][139][138] Another problem that the TTC must cope with following a heavy snowfall is that motorists park cars too close to streetcar tracks because snow banks narrow streets.