The line was closed due to damaged tracks at Lochailort after extreme rainfall caused a nearby stream to overflow.
Engineers have worked to replace more than 1,600 tons of material and re-laid 80 metres of track.
Work has also been carried out to improve drainage on third-party land to reduce future risk to the railway.
Liam Sumpter, Network Rail Scotland route director, said: “With the easing of lockdown and the reopening of the tourism sector, it was vital that we complete these repairs quickly to help support the local economy in the West Highlands.
“The line had been extensively damaged, and our engineers have been working around-the-clock to reopen the railway for our customers.
“I’d also thank our contractors – QTS and Story – for their close collaboration during this project, which has been vital to getting passengers moving again.”
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