In 2009, Kushner founded Thrive Capital, a private equity and venture capital firm that focuses on media and internet investments. Since its founding, Thrive has raised $200 million from prestigious institutional investors, such as Princeton University, Wellcome Trust, and Hall Capital.
 
The New York Times reported in September 2012, that Kushner raised $150 million for the firm’s most recent fund- Thrive III $150. Previous funds included the $40m Thrive II, which was raised in late 2011.
 
According to a profile in Forbes, Thrive was one of three firms (joining the well known Sequoia Capital and Greylock Partners) to invest in Instagram's $50 million Series B round at a valuation of $500 million. Forbes wrote that after Instagram sold to Facebook, "Thrive had doubled it money in 72 hours."
 
For his work with Thrive, Joshua was named to Forbes’ 30 under 30 list and Vanity Fair’s Next Establishment.