In 1991 Forrest married Nicola Maurice, daughter of Tony Maurice who was a major figure in the Australian League of Rights white-supremacist Christian organisation. Nicola’s sister, Katrina, is the wife of David Thompson who was the leader of the New Zealand League of Rights in the early 1980s and the leader of the Australian League of Rights during the 1990s. Forrest and David Thompson became friendly associates with Forrest appointing Thompson to a managerial role while he was on the board at Anaconda Nickel.

Forrest owns the 58.2-metre (191 ft) yacht Pangaea (named after the supercontinent that existed between 335 million and 175 million years ago). The yacht was built by US shipyard Halter Marine in 1999, and it is registered to Montego Bay, Jamaica.

After stepping down as Chief Executive Officer of FMG to reflect that he had been spending more than 50% of his time on Indigenous philanthropy, and to hand leadership reins to Nev Power, the former head of engineering company Thiess, he became Ambassador of the Australian Indigenous Education Foundation (AIEF). Encouraged by the philanthropic work of the Rockefeller Group, Warren Buffett, and Melinda and Bill Gates, Forrest founded the Australian Children’s Trust with his wife Nicola in 2001. He also started the GenerationOne project, which was founded as a result of his hero and first mentor outside his father, Scotty Black. Forrest obtained assistance from James Packer and Kerry Stokes, who each donated $2 million, along with the support of their respective media stations, Channel 9 and Channel 7. The organisation works with the Australian Children’s Trust to help create sustainable solutions on addressing social disadvantage.

In 2003, he took control of Allied Mining and Processing and renamed it Fortescue Metals Group. He is still a major shareholder of FMG, through his private company, The Metal Group. Since then, the company has grown to possess three times the tenements of its nearest rival in Western Australia’s iron ore rich Pilbara region. Fortescue holds major deposits at Mount Nicholas, Christmas Creek, Cloudbreak, and Tongolo. In 2007, he took an interest and a directorship in Niagara Mining Limited, renamed Poseidon Nickel Limited, which had in 2006 acquired from WMC the Windara nickel deposits near Laverton, Western Australia.

In 2008 Forrest appeared on the BRW Rich 200 list, with a net worth of A$9.41 billion. In subsequent years, his wealth has varied significantly as a result of variances in Australian resources sector prices. In 2016, according to Forbes Asia, Forrest’s wealth was assessed at US$1.24, making him the 22nd wealthiest Australian. In 2017 his net worth, according to the Financial Review Rich List, was A$6.84 billion, ranking him as the sixth wealthiest Australian.

The Australian Securities and Investment Commission took legal action against FMG and Forrest. Although an initial ruling by Justice John Gilmour in 2009 found Forrest hadn’t acted in a misleading or deceptive manner, Chief Justice Patrick Keane and judges Arthur Emmett and Raymond Finkelstein of the Federal Court of Australia overturned this decision in 2011, finding that FMG and its Chairman and CEO, Andrew Forrest, had engaged in misleading or deceptive conduct and breached the continuous disclosure provisions in the Corporations Act, 2001 (Cth), by claiming to have binding contracts with China. The court found that a Chinese framework agreement does not amount to a binding contract, in the natural meaning of the word. If found to have breached director’s duties, Forrest faced the possibility of being banned as a director of an ASIC-listed company. FMG appealed against the decision, and in October 2012, the High Court found in favour of FMG and Forrest, reversing the decision of the full bench of the Federal Court and agreeing with the original 2009 decision by Justice Gilmour.

After buying back the family property, Minderoo Station in 2009 Forrest acquired the adjoining properties, Nanutarra and Uaroo Stations in 2014, increasing his total pastoral holdings in the Pilbara to 7,300 square kilometres (2,819 sq mi). In August 2015 he acquired both Brick House Station and Minilya Station for an estimated A$10 million, bringing his total pastoral holdings to over 10,000 square kilometres (3,861 sq mi).

Forrest established the Walk Free Foundation in 2010 to fight modern slavery. In 2013 the organisation launched the Global Slavery Index ranking 162 countries “based on a combined measure of three factors: estimated prevalence of modern slavery by population, a measure of child marriage, and a measure of human trafficking in and out of a country”. The Index estimates there are 29 million slaves worldwide, roughly half in India and Pakistan.

In June 2011, Allied Medical, of which Forrest owned 46%, was acquired by BioMD for over $20 million.

Forrest and his wife, Nicola, made The Giving Pledge in 2013, stating:

In 2013, Forrest was chosen to lead a review into Indigenous employment and training programs, which was to report to the Australian government. The review was delivered on 1 August 2014, with 27 recommendations, one of which was the healthy welfare card.

As of September 2007, Forrest had injected A$90 million into his children’s charity. Philanthropic activity has included gifts to his alma mater, Hale School; participation in the St Vincent de Paul Society CEO sleepouts; and a gift from the proceeds of the sale of 5,000 tonnes (5,500 short tons) of iron ore to the Chinese earthquake relief effort. In October 2013 it was announced that Forrest was to donate A$65 million towards higher education in Western Australia. At the time the sum was believed to be the highest philanthropic donation in Australia, with most going toward funding scholarships. The Minderoo Foundation, Forrest’s private foundation, was renamed as the Minderoo Group is to be expanded to include higher education contributions. The foundation has given A$270 million through the foundation since 2001. In 2017 Forrest donated $400 million to medical research and social causes, and in 2019 donated a further $655 million to expand the existing work of the Minderoo Foundation in areas including cancer research, early childhood development, ocean health, and eliminating modern slavery, the largest ever living donation by any Australian philanthropist.

Forrest acquired meat processing company Harvey Beef in May 2014 for A$40 million. The biggest exporter of beef in Western Australia, it was until August 2014 the only one accredited to export to China.

In January 2014, Forrest announced a deal with Pakistan to do away with more than two million slaves in return for cheap coal.

Andrew and Grace Forrest took part in a meeting held in 2014 in the Vatican. There was a Joint Religious Leaders Declaration Against Modern Slavery which was signed by Pope Francis, Mata Amritanandamayi, Justin Welby, Thích Nhất Hạnh, K. Sri Dhammananda, David Rosen, Ecumenical Patriarch Bartholomew, Abraham Skorka, Mohamed Ahmed El-Tayeb, Mohammad Taqi al-Modarresi, Basheer Hussain al-Najafi, and Omar Abboud: religious leaders representing forms of Christianity, Judaism, Islam, Hinduism and Buddhism.

In 2017 Forrest was appointed an Officer of the Order of Australia for distinguished service to the mining sector, to the development of employment and business opportunities, as a supporter of sustainable foreign investment, and to philanthropy.

In 2020, Forrest acquired both Quanbun and neighbouring property, Jubilee Downs, in the Kimberley region of Western Australia for over A$30 million.