CIMIC Group Limited (formerly Leighton Holdings) is an engineering-led construction, mining, services and public private partnerships leader working across the lifecycle of assets, infrastructure and resources projects.

Founded in 1949 by Stanley Leighton, Leighton Holdings was first listed on the Melbourne Stock Exchange in 1962. The company formed Leighton Asia, based in Hong Kong, in 1975.

In July 1983 Leighton Holdings, purchased Thiess Contractors, with its major shareholder, Hochtief, becoming a shareholder in Leighton Holdings. In April 1997, the Welded Mesh structural materials division was sold to Smorgon Steel.

In 2000, Leighton Holdings bought a 70% stake in John Holland; this was increased to 99% in 2004 and 100% in December 2007. Hochtief became a majority shareholder of Leighton Holdings in February 2001.

In October 2013, Fairfax Media alleged that Leighton Holdings had made corrupt payments to Hussain al-Shahristani, Deputy Prime Minister of Iraq, to secure an oil pipeline contract in Iraq and other contracts. Basil Al Jarah, the Iraq country manager for Unaoil, a Monaco-based company allegedly acting for Leighton Holdings, subsequently pleaded guilty to corruption.

By March 2014, Spanish company ACS Group, through its acquisition of a majority shareholding in Hochtief, was the majority owner of Leighton Holdings. In June 2014, Verdes also became chairman of Leighton's executive board.

In December 2014, Leighton Holdings sold John Holland to China Communications Construction for $1.15 billion.

In April 2015, Leighton changed its name to CIMIC Group (abbreviated from Construction, Infrastructure, Mining and Concessions).