GTCR is seeking to raise $6.75 billion for a buyout fund that would be its biggest yet, according to a person with knowledge of the matter.
The firm has begun preliminary discussions with prospective investors, said the person, who requested anonymity because the talks are private.
A spokeswoman for GTCR declined to comment.
The Chicago-based firm raised $5.25 billion for its 12th buyout fund, which closed in October 2017 and marked GTCR's largest fundraising to date.
"We have the organizational capacity to pursue more and potentially larger-scale investment opportunities," Craig Bondy, a managing director, said at the time.
The firm has traditionally focused on five sectors: technology, business services, media and telecommunications, health care and financial services and technology. It announced this month an agreement to acquire Xermelo, an oral therapy for carcinoid syndrome diarrhea.
In July, GTCR agreed to sell Optimal Blue, a digital marketplace for mortgages, and in June announced the purchase of software maker Citra Health Solutions.