On Assignment Inc. said Monday it is acquiring a majority interest in Los Angeles specialty staffing firm Creative Circle LLC for $570 million in cash and equity – and an additional $30 million if performance benchmarks are met.

Privately held Creative Circle will add expertise in digital marketing, advertising, and graphic design workers to the Calabasas staffing firm’s portfolio of information technology and engineering professionals.

Creative Circle, headquartered in Mid-Wilshire, had revenue of about $226 million last year and has posted compounded annual growth of 26 percent for the last three years. A Morgan Stanley-affiliated private equity fund previously owned the stake purchased by On Assignment.

Peter Dameris, On Assignment’s chief executive, said the acquisition will help the company achieve its goal of $3 billion in annual revenue by 2018. The company had revenue of $1.86 billion last year.

“Our two companies share a common goal of putting people to work in challenging roles and the timing could not be better as the lines between IT and marketing departments are starting to converge,” Dameris said in a statement.

Dennis Masel, Creative Circle’s chief operating officer, said that the two companies share similar cultures and vision.

“As we analyzed how best to continue to grow our company, joining On Assignment quickly became the logical choice,” he said in the statement.

The deal is expected to close before the end of the second quarter.

Shares closed up $4.76 or about 14 percent, to $37.60 on the New York Stock Exchange.