The project gave rise to the EMB 121, named Xingu—after the river that originates in Mato Grosso and flows into the Amazon, passing through Brazil's first demarcated indigenous reserve, the Xingu Indigenous Park. Designed to serve the executive transport market, it had a capacity of up to eight passengers and was the first pressurized aircraft designed and built in Brazil. This feature allowed it to fly at an altitude of 28,000 feet—above cloud formations and atmospheric turbulence—while maintaining an internal cabin pressure equivalent to 8,000 feet, thereby ensuring greater passenger comfort.

In addition to cabin pressurization, the Xingu introduced other significant technological advancements to the Brazilian aviation sector, such as the "T-tail" configuration, in which the horizontal stabilizer assembly was mounted atop the vertical stabilizer. This setup prevented propeller wash from striking the horizontal stabilizer, resulting in reduced vibration and noise levels. The design also served as a distinguishing feature of the EMB 121; with its elongated nose, the aircraft resembled a jet. It was further notable for its low fuel consumption—requiring only one-quarter of the fuel needed for a comparable jet. Moreover, it could operate on short runways, as it shared the same landing and takeoff characteristics as the Bandeirante (which was designed for small airfields) yet offered a higher cruising speed than its predecessor.

Construction of the first Xingu prototype began in 1976, and it made its maiden test flight—without the pressurization system engaged—on October 22 of that year. The prototype was officially unveiled at Embraer weeks later, on December 4. In May 1977, the Xingu successfully completed its first test flight with the pressurization system engaged.

The first buyer was the Brazilian Air Force (FAB), intending to equip the Special Transport Group (GTE) based in Brasília. However, a significant portion of Embraer's focus was directed at the international market: 28 of the 32 units produced annually were to be marketed by the U.S.-based Piper Aircraft Corporation, ensuring technical maintenance availability worldwide and expanding the aircraft's commercial reach.

The first Xingu prototype was painted in Copersucar-Fittipaldi livery, as the aircraft had been loaned to the Formula 1 team for promotional use in Europe, the United States, and Canada. This prototype became the first domestically manufactured aircraft to cross the Atlantic—flying alongside a Bandeirante in Air Littoral livery—on May 26, 1977. The aircraft took off from São José dos Campos bound for Paris; they made a technical stop in Fernando de Noronha and, the following day, departed for Dakar before continuing to Seville and finally Paris. Piloted by Luiz Carlos Miguez Urbano and Túlio Silviano Brandão, the Xingu completed the journey in six hours and forty-five minutes—nineteen minutes faster than the Bandeirante.

The aircraft were exhibited at the Le Bourget International Air Show, marking Embraer's first appearance at the event.

About two years later, on August 30, 1979, the Xingu was rolled out. The aircraft was acquired by various companies, such as the British firm CSE Aviation. Its success was such that, as part of Embraer's tenth-anniversary celebrations in 1979, a commemorative stamp featuring the Xingu—which was named the 1980 Aircraft of the Year—was issued.

Its civil certification was finalized in June 1979. Later that same year, its de-icing system received certification in the United States. With this certification, the Xingu was launched on the international market, where it was subsequently very well received. In France, for instance, the aircraft has been used for pilot training since 1983, and the French Air Force decided to extend its service life until 2025 through the modernization of its electronic systems. This will keep the Xingu aircraft in operation for 42 consecutive years—a rarity in the industry.