Madge Elliot and family members took a trip on the Borders Railway line, which opens to the public on 6 September.
The new railway will restore passenger services from Edinburgh to Tweedbank for the first time since 1969.
Mrs Elliot fought to save the Waverley Line between Edinburgh, Hawick and Carlisle before it closed in the 1960s.
She led a petition to keep the line open and in 1968 - along with son Kim and MP David Steel - hand-delivered it to Harold Wilson, the prime minister at the time.
However, her efforts were unsuccessful and the line closed on 6 January 1969.
In 1999 she helped found the Campaign for Borders Rail, a grassroots group which pushed for the restoration of rail services to the Scottish Borders.
In June this year a locomotive was named after her to mark her efforts.
The rail link was restored after a deal was agreed between Transport Scotland and Network Rail in 2012.
On Sunday, Mrs Elliot and her family travelled from Tweedbank to Newcraighall and back during driver training.
She told BBC Scotland: "This is wonderful. Mind you, I never had any doubt it would come back again. It was such a daft thing to do, to close our railway.
"The scenery is absolutely beautiful. We can attract visitors from all over the world to this part of the country."
Her elder son Kim said: "We're delighted to be among the first people to travel on the new Borders line as this railway is so important to our family.
"Experiencing the route first-hand is something we've all been looking forward to since the Borders Railway deal was concluded in 2012 and it's great to see my mother being honoured for the role she played in the re-opening of the line."
Infrastructure Secretary Keith Brown said: "It was a real privilege for me to meet Madge when we named a locomotive in her honour and to put her forward to experience the route before it opens.
"Madge Elliot is a legend of the Borders and the railways, and it is absolutely fitting that she be the first member of the public to travel on this line as she was so instrumental in having it reinstated.
"We're now only weeks away from seeing what will be a truly historic event in the opening of the Borders Railway, with all of the benefits that will bring, and I look forward to joining Madge and the rest of the Borders, Midlothian and Edinburgh communities for that celebration."
An 87-year-old who campaigned to bring a railway line back to the Borders has become one of the first passengers to travel on the new service.