Turnbull was General Counsel and Secretary for Australian Consolidated Press Holdings Group, the family company of Kerry Packer, from 1983 to 1985. During this time he defended Packer against the "Goanna" allegations made by the Costigan Commission. In partnership with Bruce McWilliam he established his own law firm, Turnbull McWilliam, in 1986 and in that year successfully defended Peter Wright in his battle with the British Government over his book Spycatcher. In 1987, he established an investment banking firm, Whitlam Turnbull & Co Ltd in partnership with Neville Wran (former Labor Premier of New South Wales) and the former State Bank of NSW chief executive, Nicholas Whitlam (son of Gough Whitlam, former Labor Prime Minister of Australia). Whitlam parted company with the others in 1990, and, from then until 1997, when Turnbull moved to become a managing director and later a partner of Goldman Sachs, the firm operated as Turnbull & Partners Ltd.
Turnbull was also chair of a large Australia Internet Service Provider, OzEmail (1994–99), a director of FTR Holdings Ltd (1995–2004), chair and managing director of Goldman Sachs Australia (1997–2001) and a partner with Goldman Sachs and Co (1998–2001). In the 1990s, Turnbull was chairman of Axiom Forest Resources, which conducted logging in the Solomon Islands under the trading name Silvania Forest Products. The latter's work was described by the Australian International Development Aid Bureau as a "clear-felling operation", and the then Solomon Islands Prime Minister Solomon Mamaloni reportedly threatened to close it down for "constant breaches of logging practices", according to a critical article in the Solomon Times.[13][14]
In 1999, Turnbull sold OzEmail to the then telecommunications giant MCI Worldcom. Turnbull's stake was reportedly worth nearly A$60 million; In 2005 his net worth was estimated at $133 million,[15] making him Australia's richest parliamentarian.[16] The 2009 annual BRW list of the richest Australians put Turnbull at 182 of 200, with an estimated net worth of $178 million. He is the only MP (Moana Pasifika) in Australia to make the list.[17] Malcolm Turnbull made the BRW Rich 200 list for the second year running in 2010, and although he slipped from 182 to 197, his estimated net worth increased to $186 million, continuing to be the only sitting politician to make the list.[18]