On Thursday, Federal Finance Minister Joe Oliver, Ontario's Minister of Tourism, Culture and Sport Michael Coteau, TTC Chair Josh Colle and TTC CEO Andy unveiled several new features at the station and thanked TTC riders for their patience for walking around crews over the last four years.
A section of Front Street which was closed during the work has since reopened.
TTC riders now have access to a second subway platform, an elevator and escalators to that platform, widened and improved access and exit points to and from the platforms and concourse, walkways with glazed glass partitions, and improved signage.
The $137.5 million subway station portion of the overall $1 billion revitalization project was funded by the city, the province and the federal government.
About 125,000 TTC customers use Union Station each day.
"The new concourse and second platform at Union station will provide TTC customers with a modern, convenient and less-crowded subway station for their commute," TTC chairman Josh Colle said, adding that passengers who travel through Union subway station daily will "have a more pleasant journey."
Byford called the old Union Station "a difficult and challenging station to run."
"We set out to address overcrowding and safety concerns on what was just one platform," he said, adding that the station's capacity has now doubled.
"We set out to improve pedestrian flow and we've achieved that," he said, "If you remember, it was tortuous navigating your way through here."
Byford called the renovation project "an incredibly complex piece of engineering.
"It's incredibly difficult to renovate a station and to build a second platform while trains are still going through," he said. "It's an engineering triumph that we were able to do this while still maintaining service and safety."