The line was re-opened for passenger trains on Friday, but customers were urged only to travel if their journey was essential as services on the line were severely limited by ongoing RMT strike action.
Engineers had been working around-the-clock to repair and re-open the line since heavy rain on December 30 caused a landslip beneath the tracks – destabilising the foundations of the railway.
Over the last week, work has been undertaken to remove hundreds of tonnes of loose material from beneath the line, regrade the slopes and install over 300 tonnes of new stone to stabilise the embankment.
The track has also been relaid and signalling systems were tested ahead of the line re-opening on Friday.
Liam Sumpter, Network Rail Scotland route director, said: “Our engineers have worked as quickly as possible to complete these repairs and re-open the railway.
“This was a very challenging project, with hundreds of tonnes of material having to be removed and significant repairs made to over 40 metres of the railway.
“We appreciate the inconvenience the closure of the line has caused and we thank everyone for their understanding during these recovery works.”
Barry Milsom, executive director of operations and safety at Avanti West Coast, said: “We’re pleased the West Coast Mainline has now re-opened north of Carlisle following repairs to the tracks.
"We would like to thank our customers for their patience and understanding while Network Rail carried out this urgent work.”
Services returned to normal on Sunday, following a reduced timetable on Friday and Saturday due to the on-going strike.
The RMT Union is calling on the UK Government to unlock the negotiations.
General secretary Mick Lynch said: “I want to see the government stop play-acting because the truth, written in black and white in their rail contracts, is that they’ve been in complete control of this dispute from day one. The train operators cannot move without government say so."