Shotts, run by Ian Irvine and his son Ian junior, was founded in 1989 and operates from a 10-acre site. Its latest published accounts show a profit of £20,000 in 2012. The value of the deal was not disclosed.
Manheim, a subsidiary of Atlanta-based media conglomerate Cox Enterprises, owns the motors.co.uk website and has more than 130 car 'remarketing' operations including 38 sites in Europe, one of them in Glasgow.
Last July it snapped up Glasgow-based Kingfisher Systems, a developer of online auction software.
Mr Irvine is appointed regional director of Manheim Scotland and its management and staff are to be transferred to the new owner under TUPE regulations.
Michael Buxton, chief operating officer of Manheim UK, said Shotts had built an excellent reputation, especially within the corporate sector.
He commented: "After some weeks of inevitable uncertainty, we're pleased to have confirmed this deal which is good news for the motor trade in Scotland."
Mr Irvine said Shotts had "considered all the options", adding: "Being part of the world's biggest vehicle remarketing business gives us the assurance, insight and financial backing to grow Manheim's market share in Scotland." He said longer-term the business would "develop a series of services" to meet customer needs.
Manheim already has 17 auction centres in the UK.