The first railway line to arrive in Ottawa was the Bytown & Prescott Railway in 1854. It ran from Prescott to Montreal Road. There's been a story that the railway company ran out of rails and had to use wooden blocks with iron straps to finish the line. In reality, the railway ordered enough rails to complete the railway.

In January 1855, the line was completed with an extension to Sussex Street (now Sussex Drive). The line officialy opened on 10 May 1855.

In 1856, the Bytown & Prescott Railway changed its name to the Ottawa & Prescott Railway.

On 15 September 1870, the Canada Central Railway opened a line from Carleton Place to Broad Street.

By 1871, the Ottawa & Prescott Railway became the St. Lawrence & Ottawa Railway. On 13 December 1871, the St. Lawrence & Ottawa Railway opened a line connecting the existing line to the Chaudière yards.

The Prince of Wales Bridge was opened with the Québec, Montréal, Ottawa & Occidental Railway extending its line to the Chaudière yards from Hull.

1883 saw the Canada Atlantic Railway complete a line from Coteau Québec to the Chaudière yards. The first section, terminating at Elgin Street, opened on 13 September 1882. The remaining section of the line was completed in December 1883 to Broad Street.

On 18 September 1893, the Ottawa, Arnprior & Parry Sound Railway opened a line from Ottawa to Arnprior. The entire line to Parry Sound was completed by October 1894.

Between 1895-1896, the Ottawa, Arnprior & Parry Sound Railway and Canada Atlantic opened a line along the canal toward Rideau Street. The Central Depot was opened on 17 September 1896 at the end of this line.

In 1898, the Ottawa & New York Railway arrived with a new line from Cornwall to Ottawa.

On 26 April 1900, a chimney fire in Hull soon spreaded into a huge conflagration which consumed much of Hull and almost all of Lebreton Flats. The fire took much of the Chaudière yards with about 188 freight cars destroyed and the Canadian Pacific Union Station and freight sheds destroyed as well.

However, the railway and lumber yards in Ottawa quickly recovered and by the end of the year, passenger service resumed to Broad Street with a new Union Station.

In 1901, the Royal Alexandra Interprovincial Bridge is opened and the first train crossed the bridge on April 22.

The Canadian Northern Ontario Railway opened a line from Hawkesbury to Ottawa (at Henderson Avenue) and service commenced between Montreal and Ottawa on 5 December 1909.

On 1 June 1912, the Grand Trunk Railway (GTR) opened its Central Station (later known as Union Station) along with the its hotel the Chateau Laurier. The grand opening was subdued due to the death of GTR's president Charles Melville Hays on the RMS Titanic on 15 April 1912.

The Canadian Northern Ontario Railway opened a line from Napanee to Hurdman on 3 December 1913.

The Canadian Northern Ontario Railway opened a line from Pembroke to Ottawa on 23 November 1915.

1915 marked the start of rail's height in Ottawa. Ottawa's rail network would remain this way throughout the 20's and most of the 30's.

The first major railway line abandoned in Ottawa was the Canadian National Railway (originally Canadian Northern Ontario Railway) from Hawkesbury to Hurdman.

A section of the Renfrew line was abandoned from Island Park Drive to a new connection called Nepean Junction (just north of Corkstown Road).

In 1950, Jacques Gréber completed a plan for the National Capital Region which would drive urban planning in the region for the next 50 years. Part of the plan included removing railway lines out of the downtown and into the suburbs.

One of the first steps in the plan was the creation of the Walkley Trainyards. The Walkley Line was opened by Canadian National on 19 November 1953 and most freight was redirected along this line.

On 16 February 1957, New York Central Railroad, that took over the Ottawa & New York Railway, abandoned the line from Ottawa to Cornwall. A short section was retained by Canadian National as the Ramsayville Spur.

In 1960, Canadian National abandoned the section of the Renfrew line between Bayswater Avenue and Preston Street. That same year, the Uplands spur is also abandoned.

The years 1961 and 1962 saw the removal of the Renfrew line from the Rideau Canal to the Chaudière yards.

By 1967, the railway plans of the Gréber Plan were nearing completion as all the railway lines were removed from the downtown and replaced with parkways and expressways.

In 1963, the remaining Renfrew line in the downtown was abandoned.

1966 saw the most significant changes with the following:

- removal of the original Ottawa & Prescott Railway line from Sussex Drive south to Bank Street

- the creation of a Hawthorne Connection just east of Sheffield Road

- the removal of tracks from Hurdman to Union Station along the canal

- the removal of tracks over the Interprovincal Bridge.

Also, a new Ottawa Station was opened on 31 July 1966 near the suburb of Alta Vista. The old Union Station was saved from demolition and became the Government Conference Centre. Currently it houses the Senate while renovations are taking place at the Centre Block of the Parliament Buildings.

By 5 August 1967, the tunnel under Dow's Lake and its below grade approaches were complete.

By 28 August 1967, Canadian Pacific Railway abandoned part of the Carleton Place line from Bells Corners to McRae Avenue.

In October 1967, Canadian Pacific closed the Ottawa West Yard and moved freight to the Walkley Yards.

Canadian Pacific abandoned a section of the Carleton Place Spur between McRae Avenue and Ross Avenue.

Two minor changes occurred in 1972. Canadian Pacific removed a section at Ellwood Junction and the Ramsayville spur was abandoned by Canadian National.

Canadian Pacific removes the last section of the Carleton Place spur between Ross Avenue and Bayview Road.

Canadian Pacific abandoned the last of the Sussex Street line between Bank Street and Ellwood.

On 9 August 1986, Canadian Pacific abandoned the Montréal and Ottawa line between Rigaud and Ottawa.

On 15 January 1990, Canadian Pacific adandoned the Carleton Place line from Nepean to Carleton Place.

Canadian Pacific abandoned the Ottawa Airport spur this year.

Canadian Pacific abandoned the Prescott line from Leitrim Road and Kemptville.

On 15 October 2001, the City of Ottawa began light-rail service along the railway line going under Dow's Lake between Bayview and Greenboro. The new service was called the O-Train.

On July 2002, the tracks for the express sheds at Terminal Avenues were abandoned back to Lancaster Road.

Canadian National abandoned its railway line from Nepean Junction to Pembroke.

On September 14, 2019, the Confederation Line of the O-Train opened between Tunney's Pasture Station and Blair Station.