An investigation is under way after a tree fell onto overhead cables as contractors cleared trackside vegetation.
The incident at Hyndland in the West End severely disrupted rail services on Tuesday for thousands of passengers.
Many services running west in and out of Queen Street and Partick suffered delays and some were cancelled.
Services between Airdrie and Balloch, and Cumberland and Dumbarton Central were suspended.
The damage was caused as routine work was being undertaken to safeguard the line from dangerous trees and vegetation that could have posed a risk to services.
The tree came down at around 3.45pm as contractors hired by train operators and Network Rail were working near Gartnaval Hospital.
Repairs were almost complete by 10pm last night and services were expected to have resumed by 11pm Tuesday.
Remaining services were expected to return to normal after then and run as timetabled for Wednesday morning.
A ScotRail spokeswoman said: “The ScotRail Alliance works constantly to keep the rail network free from overgrown vegetation that can cause damage to overhead lines or trains.
“This incident involved a third party contractor working alongside the line.
“There will be an investigation into what happened to try to prevent this sort of incident in future.”
Bus services were brought in to ferry some passengers between stations.
ScotRail said refunds would be offered in extreme cases.