Kohlberg Kravis Roberts, the owner of Willis, is to sell off a chunk of its shares in the insurance broker.
It announced its intention to sell $450m-worth (£307m), or about 10% of its stake, which currently stands at 53%.
Following the sale, it will remain the largest shareholder.
The sale is likely to net a handsome return for KKR on its investment in Willis, which it bought for $3 (£2.05) a share in 1998.
Willis' shares were trading at $24.50 (£16.70) on Tuesday.
When Willis returned to the stock market in June last year, the shares sold for $13.50 (£9.20).