Atlantic Trust manages roughly US$20 billion in assets on behalf of high-net-worth individuals, families, foundations and endowments across the United States.
"This transaction further enhances our private wealth management offering to high-net-worth clients and is consistent with our acquisition of MFS McLean Budden in Canada," said Victor Dodig, CIBC's group head of wealth management.
"It also strengthens our position in the U.S. market where we have established a presence in asset management through our separate and strategic investment in American Century."
The deal, subject to regulatory approval, is expected to close in the second half of 2013.
The bank said the acquisition will add to its adjusted earnings per share in its 2014 financial year.
CIBC had signalled last month that it wanted to expand its wealth management business particularly in the United States.
The bank's chief financial officer, Kevin Glass, told a financial services conference that the bank would like the sector's contribution to reach 15 per cent of overall earnings, up from the current level of 10 per cent achieved in 2012.