It provides telephone and data services to users worldwide, via portable or mobile terminals which communicate with ground stations through fifteen geostationary telecommunications satellites.

The company was listed on the London Stock Exchange until it was acquired by Connect Bidco, a consortium consisting of Apax Partners, Warburg Pincus, the CPP Investment Board and the Ontario Teachers' Pension Plan, in December 2019.

[5][7] In coordination with the International Civil Aviation Organization in the 1980s, the convention governing INMARSAT was amended to include improvements to aeronautical communications, notably for public safety.

[8] In the mid-1990s, many member states were unwilling to invest in improvements to INMARSAT's network, especially owing to the competitive nature of the satellite communications industry, while many recognised the need to maintain the organisation's older systems and the need for an intergovernmental organisation to oversee public safety aspects of satellite communication networks.

[19] Following privatisation in 1999 Inmarsat developed and launched the first satellite communications system offering global coverage, BGAN.

[21] In the 2010s, Inmarsat began development of the High Throughput Satellite (HTS) constellation Global Xpress, operating in the Ka-band portion of the spectrum.

[22][23] In 2017, Inmarsat launched its first S-band satellite, intended to provide (in association with an LTE ground network) inflight internet access across Europe.

[24] In March 2018, Inmarsat partnered with Isotropic Systems to develop a state-of-the-art, all electronic scanning antenna intended to be used with the Global Xpress network.

[25] On 20 September 2018, Inmarsat announced its strategic collaboration with Panasonic Avionics Corporation for an initial ten-year period, to provide in-flight broadband for commercial airlines.

[29] In November 2019, Inmarsat rejected an eleventh-hour effort to derail the US$6 billion sale, in which it was accused of ignoring a potential boost to the company's value.

[33] Viasat has promised to honour a pledge made by the previous owners, when it was taken private in 2019, that Inmarsat would remain a UK-based company, and for other planned investments.

[34] Provisional approval for the merger was given by the UK's Competition and Markets Authority in March 2023[35] with 25 May 2023 set as the date for a formal decision.

[46] Newer Inmarsat services use an IP technology that features an always-on capability where the users are only charged for the amount of data they send and receive, rather than the length of time they are connected.

Use of regional beams allow user terminals (also called mobile earth stations) to operate with significantly smaller antennas.

Country codes phased out on 31 December 2008 were Since 18 July 2017, Inmarsat users using the service provided by China Transport Telecommunication & Information Center may apply for 11 digits Chinese mobile phone numbers starting with 1749.

Advanced services are provided via distribution partners but the satellite gateways are owned and operated by Inmarsat directly.

These satellites planned to offer both Ka- and L-band payloads and additional capacity to the existing BGAN and Global Xpress networks.

[99] The second satellite Inmarsat-6 F2 (GX 6B)[100] was launched on 18 February 2023 on a Falcon 9 Block 5 rocket, but suffered a power system failure in orbit that prevented it from becoming operational.

[106] In March 2014, Malaysia Airlines Flight 370 disappeared with 239 passengers and crew en route from Kuala Lumpur to Beijing.

[107][108] In conferences given by French engineers and pilots Jean-Luc Marchand and Patrick Blelly stated that the company tried to reach, several hours after plane disappeared, the airplane by ringing the satellite phone onboard.

[109] The attacks on US Embassies in Nairobi (Kenya) and Dar es Salaam (Tanzania) in summer of 1998 were organized parly through satellite communications.

[110] Osama bin Laden asked one of his staff to acquire a Mini-M satellite phone in London, using cash of about US$10,000 to US$15,000 which had been sent to several Al-Qaeda members.

[112] His phone number, which was 00-873-682505331,[113] (00 for international, 873 for Indian Ocean based sat coverage, 682505331 as the line) was disclosed during a trial of bombings in US embassy in Kenya.