Portfolio Recovery Associates UK (PRA) anticipates the new jobs at its Kilmarnock offices as part of a £1.2 million taxpayer-funded package.
Growth is expected in extra call centre jobs and other roles, according to chief executive Steve Fredrickson.
Among its services, PRA tries to recover unpaid bills from consumers who may have fallen behind.
First Minister Alex Salmond announced the investment during an official visit to the US as part of the annual Scotland Week.
"PRA UK is a well-known employer in Kilmarnock and the announcement of hundreds of new jobs is fantastic news for the area," he said.
"Last month, the Scottish Cabinet met in Ayrshire where we focused on community regeneration announcing funding of £1.7 million to help the area flourish."
Douglas Reid, leader of East Ayrshire Council, welcomed the investment.
"This employment on a large scale is just reward for the effort we are putting into economic development, and I would encourage any company with growth plans to come and talk to us," he said.
"I know that local people will make the most of this exciting opportunity, looking ahead to a great future for Kilmarnock and East Ayrshire."
Local SNP MSP Willie Coffey said: "Scotland has a strong track record of attracting investment and today's announcement goes to show that Scotland is a place where international companies want to come and do business."
The funding, known as Regional Selective Assistance, is being awarded through Scottish Enterprise, an agency of the Scottish Government. The type of grant is typically made over several years as job and other targets are met, the Government said.