Formerly a dual-listed company with listings on the Copenhagen and London stock exchanges, G4S was purchased by Allied Universal in April 2021.

[12] In 2006, 2007 and 2008, G4S was the subject of a global campaign by union workers alleging that its subsidiaries undermine labour and human rights standards.

[14] The 2006, US State Department Report on Human Rights in Indonesia, released in March 2006, featured the ongoing dispute in Jakarta with Group4/Securicor.

[16] The company disputed these claims and pointed to its strong relationships with unions around the world, including the GMB in Britain.

[17] In March 2008, it was announced that G4S were taking over Scottish Rock Steady Group – who steward at major sporting and music events mostly in the UK.

[18] In April 2008, G4S acquired RONCO Consulting Corporation, one of the world's premier humanitarian and commercial mine action, ordnance disposal and security companies.

[24] Simultaneous to this, G4S and the SEIU reached an agreement to end their long dispute and establish a framework to work together in the interest of employees.

[25] In 2009, G4S continued to acquire companies: Secura Monde International and Shiremoor International Engineering, together, the UK's leading specialist banknote and high security technical and commercial advisory companies; All Star International for $60 million,[26] one of the premier facilities management and base operations support companies providing services to the US government; Adesta, US-based provider of integrated security systems and communication systems; and Hill & Associates Consultants Limited, Asia's leading provider of specialist risk-mitigation consulting services.

[27][28] In the autumn of 2009, G4S personnel in Australia went on strike, arguing that the company had subjected them to low pay and poor working conditions.

[35] G4S's chief, Nick Buckles, recounted the events of the failed acquisition, which cost the company tens of millions of dollars, as "...one of the most bruising experiences of my life".

[36] A combination of institutional investors who led the response and the minority shareholders who followed, objected to a variety of factors, not the least of which was the additional leverage and debt the deal would introduce to G4S's balance sheet.

[41] Shares in G4S later dropped nine percent after the firm claimed it faced a possible £50 million loss as a result of failing to provide sufficient trained staff for the 2012 Olympic Games.

[42] On 17 July, the company's chief executive, Nick Buckles, appeared before the Home Affairs Select Committee, where he apologised for the organisational failings, expressed regret at having taken on the Olympic security contract, and agreed in principle to pay bonuses to soldiers drafted at the last moment as replacement security staff.

[43] Pressed by Labour MP David Winnick, he was forced to admit that organisational situation had become a "humiliating shambles".

[49] Subsequent to the Olympics contract failures, the chief constables of Bedfordshire, Cambridgeshire and Hertfordshire were to recommend abandoning outsourcing work to G4S.

[53] G4S was in the news in June 2016 because of employee Omar Mateen, the gunman behind one of the worst mass-shooting incidents in United States history (where 49 were killed),[54] who was employed as a security guard by the company.

Skipper, who was the warden at institution, wrote that "in light of the tragic events at Virginia Tech officer Mateen's inquiry about bringing a weapon to class is at best extremely disturbing".

He was said to have passed a psychological test and medical exam performed by Dr. Syed Shafeeq Rahman, who had close ties with Mateen's family.

G4S admitted Mateen's form had a "clerical error", and clarified that he had instead been cleared by Rahman, who was from the same firm that bought the wrongly-named doctor's practice.

[70] Ben Saunders, the head of two British immigrant centres that have been the focus of abuse of detainees was put on leave in September 2017.

Saunders had previously directed the Medway Secure Training Centre where juveniles had been found to have been abused before G4S had divested itself of its youth detention component.

[84] In the early 2000s, the company (then still known as Group 4 Falck) bid unsuccessfully for the right to operate several railway franchises in the United Kingdom.

[88] In 2014, the Austrian Ministry of the Interior awarded G4S a contract to run a detention center in Vordernberg; this was the first privately operated prison in Austria.

[89] One of G4S' more interesting contracts may be securing the perimeter of Homey Airport, more commonly known as Area 51, the secret United States Air Force base in Nevada.

[94][95] G4S is a founder signatory of the International Code of Conduct for Private Security Service Providers (ICoC), a multi-stakeholder initiative convened by the Swiss government.

[98] G4S provided financial, social and logistical support to a number of athletes taking part in London 2012, including Colombian cyclist and 2012 and 2016 Olympic gold medallist Mariana Pajón,[99] Kenyan long-distance runner Pauline Korikwiang,[100][101] and Estonia's former discus thrower and shot-putter, now-Indianapolis Colts defensive end Margus Hunt.