The route will now see four return trips every Saturday, Sunday and holiday Monday in a bid to keep up with demand.
As coronavirus-related restrictions began to be imposed in March, GO service was reduced throughout the transit network as ridership demand dramatically dropped.
The Toronto-Niagara route continued to be serviced by buses and “has proven to be popular on weekends,” a Metrolinx spokesperson said on Tuesday.
The trains will help ease demand on the buses, they said.
“We are continuing to monitor ridership and demand across our entire network and making adjustments as needed,” the spokesperson added.
GO train service between Toronto and Niagara continues to be suspended on weekdays, though buses are operating.
As of last Tuesday, anyone taking GO transit must wear face coverings to help stop the spread of COVID-19.