In 2007, Arnold became the youngest billionaire in the U.S.[2] His firm, Centaurus Advisors, LLC, was a Houston-based hedge fund specializing in trading energy products that closed in 2012.
[20] During the collapse of Amaranth Advisors, Centaurus is widely credited as being one of the major players on the other side of their position, returning as much as 150% in 2005.
[28] Other multi-million gifts followed to other education programs, for example to Washington, D.C. city schools for merit pay, to Teach for America, and to StudentsFirst.
[33] From 2010–2013, the Arnolds were heavily involved in the Innocence Project which led to their interest in criminal reform.
[37] In October 2018, it was reported that Arnold had spent more than $100 million in health-care related grants since 2014, with a particular focus on reducing pharmaceutical drug costs.
[38] Arnold funds Institute for Clinical and Economic Review (ICER), a nonprofit that created a formula to price drugs.
[39] Arnold also has been an influential supporter of Democrats’ efforts to pass a drug-price reform bill.
[35] The new entity is known as Arnold Ventures LLC with the charter "to remove barriers between data and decisive action, working swiftly across the policy-change spectrum.
They are on record as agreeing with some of the critiques and focus on partnering with organizations to maximize their impact without undue influence.
[45][46] Arnold Ventures' 2020 grant to trial aerial surveillance hardware by the Baltimore Police Department was subject to legal challenges but in November 2020, a federal appeals court ruled that the program was constitutional and did not invade the rights and privacy of city residents.
The NAACP and ACLU have criticized the Arnold PSA because they believe risk assessment tools actually increased the number of prisoners under the guise of criminal justice reform.
[52] John Arnold and his brother Matthew[53] tore down historical homes in the River Oaks neighborhood of Houston which led to criticism by architectural conservationists.