Former Australian prime minister Malcolm Turnbull has joined one of the world’s biggest investment firms, KKR & Co, as a global senior adviser.

The appointment is effective from 1 June, Kohlberg Kravis Roberts & Co said in a statement. KKR is one of the world’s biggest private equity firms and is responsible for some of the biggest international buy-out deals in history.

Turnbull, 64, served as Australia’s 29th prime minister from September 2015 to August 2018, when he was ousted in a leadership battle.

The appointment marks a return to the world of finance for Turnbull, a former lawyer who held a host of high-profile corporate roles before entering politics as a local member of parliament in 2004.

In the 1990s, Turnbull was the local managing director of global investment bank Goldman Sachs.

He was also an investor in one of Australia’s first internet service providers, OzEmail, reportedly buying a stake for $500,000 in 1994 and selling it for $57m to MCI Worldcom five years later.

Turnbull had several shadow ministry and cabinet positions for the Liberal party and coalition government before orchestrating a leadership coup and becoming prime minister in September 2015.

He was himself unseated as prime minister in another leadership challenge in August 2018, one of four Australian prime ministers to be overthrown by their own party in a decade.

Turnbull’s first appointment since leaving government puts him in the company of several Australian prime ministers and senior politicians to take up financial advisory roles after leaving office.

The former Labor prime minister, Paul Keating, became an adviser to the investment bank Lazard Australia, while the former New South Wales premier Bob Carr became a consultant to the country’s biggest investment bank, Macquarie Group.

KKR counts around 18 senior advisers and 27 industry advisers who provide counsel on investment implications of trends and developments in public policy, regulation, societal needs and technology around the world.

Among the senior advisers with experience in the Asia Pacific region are former HSBC group chairman John Bond, former Qantas chairman Leigh Clifford and former Singaporean minister Lim Hwee Hua, according to KKR’s website.