Twenty-two passengers and the bus driver were taken to hospital but one man, yet to be named, died at the scene.
A police spokesman said: “We can confirm that a person has died and a number of people have been taken to hospital after a minibus overturned in the Scottish Borders.
“The incident took place on the A6089, between Carfraemill and Gordon, around 10.50am on Saturday, December 29.
“The private minibus, travelling from Newtongrange to Kelso, was carrying 23 adult passengers plus the driver.
“One person was sadly pronounced dead at the scene and their next of kin have now been informed.”
The 23 casualties were taken to the Borders General Hospital in Melrose, Edinburgh Royal Infirmary and Queen Elizabeth Hospital in Glasgow for treatment.
Police declared the collision a major incident and worked with partners in the Scottish Ambulance Service and Scottish Fire and Rescue Service to provide assistance to those involved.
The road remains closed in both directions while investigations take place.
Chief Inspector Steven Duncan of the Lothians and Scottish Borders Police Division said: “We’re providing ongoing support to the family of the man who tragically lost his life, along with those who have been injured and their families.
“Our road policing unit, together with partners, are currently working to establish the full circumstances surrounding this.
“We’d ask anyone who may be concerned that a loved one has been affected, or anyone who could help with our investigation, to get in touch immediately via 101 and quote incident number 1369 of December 29.”