After the success of the EMB-110 Bandeirante, Embraer began the development of their first transport category airliner in 1974. The so-called Family 12X comprised three models with modular concept designs: EMB-120 Araguaia, EMB-123-Tapajós and EMB-121 Xingu. EMB-121 was the sole 12X model effectively produced. Araguaia's name was changed to Brasilia in 1979 at the official launching of the project, when at a CAAA (Commuter Airline Association of America) convention at USA several suggestions from prospective operators were collected and incorporated to EMB-120 design. Thus, a completely new aircraft – no longer related to the 12X family – was launched. No common parts from EMB 121 Xingu were used, and the capacity was revised from 24 to 30 seats. Originally designed to utilise the new 1500SHP Pratt & Whitney Canada PW115 turboprop, it was later upgraded to the 1892 ESHP PW118.
Probably the closest to a modern replacement for the DC-3 with half again as much speed, the Brasilia attracted immediate interest from many regional airlines, particularly in the USA. The size, speed and ceiling allowed faster and more direct services around the US and Europe, compared to similar aircraft. The first aircraft entered service with Atlantic Southeast Airlines in October 1985. The basic EMB-120RT was upgraded to the extended range (1,575 km) EMB-120 ER, with older aircraft retrofitted via a Service Bulletin.
On September 11, 1991, Continental ExpressFlight 2574, broke up in flight and crashed at Eagle Lake, Texas, killing all 14 passengers and crew members. The NTSB determined that missing screws on the horizontal stabilizer led to the crash.
On August 21, 1995, Atlantic Southeast Airlines Flight 529, crashed in a field near Carrollton, Georgia. Of the twenty-nine people on board, ten were killed. This was due to failure of a propeller blade and subsequent severe engine vibration and failure.
On May 21, 1997, SkyWest Airlines Flight 724, an Embraer EMB-120 (N198SW), experienced a total loss of engine power to the right engine and associated engine fire, followed by a total loss of all airplane hydraulic systems, after takeoff from San Diego International-Lindbergh Field, San Diego, California. The airplane sustained substantial damage. The 2 pilots, 1 flight attendant, and 14 passengers were not injured. Skywest Airlines, Inc., was operating the airplane as a scheduled, domestic, passenger flight under 14 CFR Part 121. The flight was destined for Los Angeles, California. It diverted to Miramar NAS, San Diego, where it landed at 14:27 hrs. Visual meteorological conditions prevailed at the time, and an IFR flight plan was filed.
On October 21, 1998, a Capital Táxi Aéreo EMB 120RT Brasilia registration PT-WKH crashed due to pilot error during final approach to Pinto Martins International Airport. The two-man crew and one passenger on board were killed, along with one person on the ground.
On May 14, 2004, Rico Linhas Aéreas Flight 4815 operated by an Embraer EMB 120ER Brasília (registration PT-WRO), en route from São Paulo de Olivença and Tefé to Manaus crashed in the forest about 18 nmi (33 km; 21 mi) from Manaus. All 33 passengers and crew died in the worst-ever accident involving the EMB 120.
On September 14, 2011, Angolan Air Force Embraer 120ER T-500 crashed while attempting to take off from Huambo Airport, killing 17 of 23 on board.
On October 12, 2011, a Nationale Regionale Transport EMB-120, registration ZS-PYO (MSN: 120245) performing a charter flight from Libreville to Port Gentil (Gabon), overran runway 21's end and came to a stop with the nose gear intact, both main gear struts bent backwards causing the engines to "pitch down" together with the wings. A few passengers sustained minor injuries, but the aircraft was damaged beyond repair and was written off.
In February 2012, Everts Air Cargo Flight 1290, lost all pitch control due to poor maintenance procedures. The EMB landed safely in Iliamna, AK without further incident.
On 27 November 2012, an Inter Îles Air Embraer EMB 120ER Brasilia (registration number D6-HUA) was underway from Moroni to Anjouan (both in Comoros Islands) on a charter flight with 25 passengers and 4 crew, when after taking off from Moroni's Prince Said Ibrahim International Airport it lost height, and while attempting to return to the airport, waterlanded 200 m (660 ft) off the coast, about 5 km north of the airport. Local fishermen rescued everybody on board. There were only minor injuries.
On 3 October 2013, Associated Aviation Flight 361, an EMB 120RT (5N-BJY), was involved in a crash on takeoff from Lagos Airport bound for Akure. The aircraft was on a charter flight taking the body of the former Governor of Ondo State, Dr. Olusegun Agagu for burial. There were at least 15 reported fatalities travelling as passengers in the burial party. Two people who survived the crash died later in hospital.
PT-ZBA 120001 Brasília's first prototype preserved at Brazilian Airspace Memorial at the entrance of São José dos Campos airport and Embraer plant.