This total is 20 per cent ahead of forecast, with 537,327 journeys made on the Edinburgh-Tweedbank line between its opening on 6 September and 23 January compared with the 450,000 expected.
A total of 1.3 million trips are forecast in the first year, with monthly figures predicted to increase over the summer.
Campaigners said they had predicted such growth and renewed their calls for the 35-mile line to be extended south to Hawick and Carlisle.
The biggest ticket sales were from Tweedbank and Galashiels at the southern end of the line, confounding claims that most passengers would come from stations nearer Edinburgh such as Gorebridge.
Rail consultant and author David Spaven said the high sales “made a mockery” of official forecasting which had led to the line being scaled back.
The ScotRail Alliance, which includes track owner Network Rail, said punctuality was improving and overcrowding easing having plagued the line following its launch.
A spokesman said 92.7 per cent of trains were now arriving within five minutes of schedule, against 85 per cent in November. In addition, 35.5 per cent of services arrived at Tweedbank “on time” – within one minute of schedule – in the four weeks to 9 January, compared to 32.7 per cent in November.
Campaign for Borders Rail chairman Allan McLean said: “Some people thought it would take years for passenger numbers on the Borders Railway to reach this level.
“Those of us who believed the railway would be an immediate success [with] passengers have been proved right.
“It’s time to extend the tracks beyond Tweedbank and bring direct economic benefits to even more communities.”
ScotRail Alliance managing director Phil Verster said: “Every opportunity to extend the railway to Hawick and Carlisle must be evaluated and could hold very exciting possibilities for us.
“We had a sense in September that Borders was going to be popular but no-one expected us to reach 500,000 passengers so quickly.”