Founder Gerry Schwartz had previously worked at Bear Stearns in New York City during the 1970s, under investor Jerome Kohlberg, Jr., who later became a founding partner of Kohlberg Kravis Roberts. Schwartz returned to Canada, where he started working with Izzy Asper.
Schwartz founded Onex in 1984 and took the company public in 1987. The firm focused on private equity investing in North America using capital from its balance sheet for the first 16 years of its history. In 2000, it started raising investment vehicles with third-party capital with the launch of ONCAP, which focuses on smaller and middle market opportunities. In 2003, the first Onex Partners fund was raised. Today[when?], the majority of Onex’ private equity investments are made through these two platforms.
In 2007, Onex invested in a credit manager, which later became Onex Credit. The platform offers various strategies, with the largest being Collateralized Loan Obligations.
In 2019, Onex acquired Gluskin Sheff + Associates, a Toronto-based wealth manager with public equity and public credit strategies.
Since its founding, the firm has generated a gross multiple of invested capital of 2.5x and a gross internal rate of return of 27% on its realized private equity investments (as of September 30, 2020).
The firm's private equity investments are made in a wide array of industries including consumer & retail, financial services, healthcare, industrials, services and technology, media & telecom. The firm prefers to have majority control over its subsidiaries and focuses on three primary investment strategies: cost reductions and operational restructurings; platforms for add-on acquisitions; and carve-outs from multinational corporations.
Other companies which Onex owns or has owned a share include Celestica, Cineplex Entertainment, Spirit AeroSystems, SMG, Sitel, American Medical Response, Hawker Beechcraft, EmCare, JELD-WEN, Carestream Health, Purolator, Husky Injection Molding Systems, Allison Transmission, Canadian Securities Institute, Cici's, Sky Chefs, BBAM, Emerald Expositions, Tomkins, SIG Combibloc Group, Clarivate Analytics, SMG, WestJet and many others.