Around half of the Piccadilly line fleet was taken out of action last month so that repairs could be carried out, causing massive disruption to services ever since.
But today, Transport for London (TfL) said a good service had resumed on the line.
A good service has resumed on the line.— Piccadilly line (@piccadillyline) December 19, 2016
TfL said there was an unprecedented need for repairs on the trains, because a longer-than-usual leaf-fall period had led to even more damage caused by wet leaves.
This wasn't helped by the fact that Piccadilly Line trains are some of the oldest on the Tube network, so they don't have the technology that can reduce the impact of braking in cold and wet conditions.
News that services are getting back to normal will be a relief to businesses up and down the Piccadilly line, who will be hoping to cash in on the newly launched Night Tube services.
There had been fears that the start date would be delayed - the RMT union at one point called for a complete shutdown of the line until the trains were all fixed - but last week, Piccadilly line trains started running a 24 hour timetable.