New Toronto Stock Exchange trading floor, circa 1937-39
TMX's LED board displaying TSX information
The Toronto Stock Exchange likely descended from the Association of Brokers, a group formed by Toronto businessmen on July 26, 1852. No records of the group's transactions have survived. On October 25, 1861, twenty-four men gathered at the Masonic Hall to create the Toronto Stock Exchange.
 The exchange was incorporated by an act of the
Legislative Assembly of Ontario in 1878.
The TSX grew continuously in size and in shares traded, save for a three-month period in 1914 when the exchange was shut down for fear of financial panic due to
World War I. In 1934, the Toronto Stock Exchange merged with its key competitor, the
Standard Stock and Mining Exchange. The merged markets kept the Toronto Stock Exchange name. The TSX opened its new trading floor and headquarters in an
Art Deco building on
Bay Street in 1937.
 In 1977, the TSX introduced
CATS (Computer Assisted Trading System), an automated trading system, and began to use it for the quotation of less liquid equities.
In 1983, the TSX vacated its Art Deco headquarters on Bay Street and moved into the
Exchange Tower. The old TSX building later became the
Design Exchange, a museum and education centre.
On April 23, 1997, the TSX's
trading floor closed, making it the second-largest stock exchange in North America to choose a floorless, electronic (or virtual trading) environment. In 1999, the Toronto Stock Exchange announced the appointment of
Barbara G. Stymiest to the position of President & Chief Executive Officer.
Through a realignment plan, Toronto Stock Exchange became Canada's sole exchange for the trading of senior
Bourse de Montréal/Montreal Exchange assumed responsibility for the trading of derivatives and the
Vancouver Stock Exchange and
Alberta Stock Exchange merged to form the
Canadian Venture Exchange (CDNX) handling trading in junior equities. The
Canadian Dealing Network,
Winnipeg Stock Exchange, and equities portion of the Montreal Exchange later merged with CDNX.
In 2000, the Toronto Stock Exchange became a for-profit company, and in 2001 its acronym was changed to TSX.
 In 2001, the Toronto Stock Exchange acquired the Canadian Venture Exchange, which was renamed the
TSX Venture Exchange in 2002; this resulted in the creation of a parent to the TSX, the
TSX Group. This ended 123 years of the usage of TSE as a Canadian stock exchange. On May 11, 2007, the
S&P/TSX Composite, the main index of the Toronto Stock Exchange, traded above the 14,000 point level for the first time ever. On December 17, 2008, for the first time in TSX history, the exchange was closed for an entire trading day due to a technical glitch.
On February 9, 2011, the
London Stock Exchange announced that it had agreed to merge with the
TMX Group, Toronto Stock Exchange's parent, hoping to create a combined entity with a market capitalization of
$5.9 trillion (£3.7 trillion).
Xavier Rolet, who is CEO of the
LSE Group, would head the new enlarged company, while TMX Chief Executive Thomas Kloet would become the new firm president. Based on data from
December 30, 2010 the new stock exchange would have been the second largest in the world with a market cap 48% greater than the
Nasdaq. 8 of the 15 board members of the combined entity will be appointed by LSE, 7/15 by TMX.
 The provisional name for the combined group would be
LTMX Group plc.
 About two weeks after Maple Group launched a competing bid the LSEG-TMX deal was terminated after failing to receive the minimum 67% voter approval from shareholders of TMX Group. The rejection came amidst new concerns raised by Bank of Canada governor
Mark Carney regarding foreign control of
clearing systems and opposition to the deal by Ontario's finance minister.
On June 13, 2011, a rival, and hostile bid from the Maple Group of Canadian interests, was unveiled. A cash and stock bid of $3.7 billion CAD, in hopes of blocking the LSE Group's takeover of TMX. The group is composed of the leading banks and financial institutions of Canada.
In March 2015, a competing exchange,
Aequitas Neo, opened for trading, listing 45 issues that had been listed only on the TSX. The new exchange aims to focus on fairness, specifically regarding what it refers to as "predatory
high-frequency trading practices". The exchange plans to list additional TSX-listed securities.