During the 1920s and 1930s, Balfour Beatty reoriented away from bus and tramway operations towards more lucrative heavy civil engineering, particularly the development of Britain's National Grid and various power stations.

Throughout the 2010s and 2020s, Balfour Beatty has been heavily involved in several major railway projects in Britain, including High Speed 2, Crossrail, and the modernisation of the Great Western Main Line.

To service this new market, George Balfour, Andrew Beatty and others formed Power Securities to finance projects, and the two companies, with their common directors, worked closely together.

[10][8] Other work during the interwar period included the standardisation of the electricity supply in Derbyshire and Nottinghamshire, and the construction of tunnels and escalators for the London Underground.

[12][11] Peacetime saw a resumption of Balfour Beatty's traditional work, which was for a time dominated by two domestic sectors: power stations and the railways.

The business was impacted by the Attlee government's nationalisation of the electric industry with relatively little compensation received; similar moves took place in Canada and East Africa that also affected the company.

[8] During 1953, a construction company in Canada was acquired by Balfour Beatty; other activities included the Mto Mtwara harbour in Tanganyika (now Tanzania) and the Wadi Tharthar irrigation scheme in Iraq.

[8] The business also continued its involvement in the energy sector, like the Anglo-Dutch Offshore Concrete venture for the North Sea oil industry, along with an increasing focus upon large overseas projects, such as Port of Jebel Ali in Dubai and the erection of the longest high voltage lines in the western hemisphere in Argentina.

[8] Also during this time Balfour Beatty was involved in an early effort to construct the Channel Tunnel, although the project was cancelled on political grounds.

[8] It also opened offices in Paisley and Leatherhead, and in 1987, it bought the Derbyshire firm of David M Adams to give it an annualised production rate of up to 700 houses.

By the middle of the 1990s, sales were down to only five hundred per year, and although no financial figures were ever published, the housing operation was believed to have suffered heavy losses.

[18] Beyond the name change, the company's business strategy shifted considerably; while it traditionally focused on the construction of infrastructure alone, Balfour Beatty diversified into the financing, operation, design and management functions as well.

[43][44] In the following year, SSL, a joint venture between Balfour Beatty and the French railway manufacturer Alstom, was awarded several signalling-related contracted cumulatively valued at €43m.

[47] Throughout the 2010s and 2020s, Balfour Beatty has been heavily involved in several major railway projects in Britain, including High Speed 2,[48] Crossrail,[49][50] and the modernisation of the Great Western Main Line.

[56][57] In March 2009, the company was found to be a subscriber to the Consulting Association, a firm which was then prosecuted by the UK Information Commissioner's Office for breaching the Data Protection Act by holding a secret database of construction workers details, including union membership and political affiliations,[58][59] and six enforcement notices were issued against Balfour Beatty companies.

[61] On 10 October 2013, Balfour Beatty was one of eight construction firms involved in blacklisting that apologised for their actions, and agreed to pay compensation to affected workers.

[63] In October 2015, during preliminary stages of the case, the eight firms did not accept the loss of earnings that the blacklisting victims had suffered,[64] but, in January 2016, they increased their compensation offers.

[67] However, some settlements were eventually agreed, and on 11 May 2016, a 'formal apology' from the 40 firms involved was read out in court and the case (Various Claimants v McAlpine & Ors) was closed.

[68] In December 2017, Unite announced it had issued high court proceedings relating to blacklisting against twelve major contractors, including Balfour Beatty.

[69] In April 2019, Balfour Beatty was suspended from the UK Government's Prompt Payment Code, for failing to pay suppliers on time.

[71] In December 2021, Balfour Beatty Communities LLC, one of the largest providers of privatized military housing to the U.S. Armed Forces, pleaded guilty to one count of major fraud against the United States.