Mercedes sports boss Toto Wolff has sold part of his shareholding in Williams to American businessman Brad Hollinger.
Wolff, boss of Mercedes since 2013, had been planning to reduce his shareholding to address concerns about conflict of interest and compliance.
Hollinger, who runs 90 hospitals in the US, has bought 5% of the company.
Hollinger will have no management involvement in Williams but has an option to purchase further shares.
He said he saw F1 as an investment and predicted that the sport was "on the cusp of another explosion in growth through social media".
Wolff said he had no plans to sell more of his shareholding, saying his role was now purely one of an investor.
The move leaves founder Sir Frank Williams owning just over 52% of Williams Grand Prix Holdings, Wolff on just over 10%, Williams' long-time partner and former technical director Patrick Head on 9% and Hollinger on 5%.
The remaining 23.7% is listed on the stock market.
Deputy team principal Claire Williams, Sir Frank's daughter, said Sir Frank had "no interest in further diluting his existing shareholding".