The purchase price was $820 million but additional transaction details were not provided.
"We set out ... to build a specialized company focused on providing advanced capabilities in the high-growth areas of signal intelligence, cyber-security and intelligence operations," said GTCR Managing Director Craig Bondy. "We are proud to see the strategic significance of Six3 get recognized in this transaction with CACI."
Six3 is based in Virginia. It was formed in July 2009 by GTCR and veteran Bob Coleman and gained a strong presence in the areas of intelligence surveillance and reconnaissance, intelligence operations and cyber security through a series of acquisitions.
"We'd like to thank GTCR for their commitment and support in developing Six3 over the last four years," said Coleman. "GTCR has been a great partner, and we are excited to work with CACI to continue supporting our customers' missions with innovative services and solutions."