Fangio was born in Balcarce, a small town near Mar del Plata in Buenos Aires Province, Argentina, to Italian-immigrant parents. He left school at 13 to work as a mechanic and opened his own garage in Balcarce after completing military service. He began racing in 1936 on a rebuilt 1929 Ford Model A and won the Argentine Turismo Carretera national championship in 1940 and 1941.
His pre-war career included extreme long-distance road races across South America that required endurance as much as speed. The 1940 Gran Premio del Norte covered nearly 10,000 km through the Andes, Bolivia, and Peru and was won by Fangio despite mechanical failures and treacherous mountain roads. A personal tragedy followed in 1948 when his co-driver Daniel Urrutia was fatally injured in a crash during the South American Grand Prix road race. Fangio believed he would never race again, but his reputation in Argentina caught the attention of the Argentine Automobile Club and the Juan Perón government, which sponsored him for a European campaign beginning in late 1948.
Fangio joined Alfa Romeo's works team for the inaugural 1950 World Championship alongside Giuseppe Farina and Luigi Fagioli. He won the Monaco, Belgian, and French Grands Prix but retired from three rounds, allowing Farina to take the title. In 1951, Fangio won the Swiss, French, and Spanish Grands Prix with the updated Alfa Romeo 159, securing his first World Championship at the season finale in Spain by six points over Alberto Ascari.
When Grand Prix racing switched to Formula 2 regulations for 1952, Alfa Romeo withdrew. Fangio drove for Maserati in non-championship races. Driving through the night from Lyon to reach a Monza race after missing a connection, he started fatigued, crashed on the second lap, was thrown from the car and sustained a broken neck. He spent the rest of the 1952 season recovering.
Returning for 1953 with Maserati against Ascari's dominant Ferraris, Fangio won at Monza and took three second-place finishes to finish second in the championship. He also won the Carrera Panamericana in Mexico in a Lancia D24, completing the course in a record 18.5 hours.
Fangio began 1954 with Maserati, winning in Buenos Aires and at Spa, before joining Mercedes-Benz from the French Grand Prix onwards when the German manufacturer returned to competition. He won six out of eight championship rounds and took his second title. For 1955, partnered by Stirling Moss, Fangio won a brutal Argentine Grand Prix in 40-degree heat — sustaining burns to his right leg from the heated chassis — and claimed a third world title after Mercedes withdrew following the Le Mans disaster in which 83 spectators were killed.
At Ferrari in 1956, Fangio won the British and German Grands Prix among others, despite a difficult relationship with Enzo Ferrari and team management. At the season-ending Italian Grand Prix, Ferrari teammate Peter Collins — who could still win the title himself — handed his car over to Fangio with 15 laps remaining rather than pursue his own championship bid. Fangio shared the second-place points with Collins and clinched his fourth championship.
Fangio returned to Maserati for 1957 and won his fifth and final championship with arguably the most celebrated drive of his career. At the German Grand Prix at the Nürburgring, a delayed pit stop dropped him 50 seconds behind the leading Ferraris of Mike Hawthorn and Peter Collins. Fangio responded with a string of fastest laps, breaking the circuit record multiple times, and overtook both Ferraris on the penultimate lap to win by three seconds. He retired from Formula One after the 1958 French Grand Prix.
Fangio won 24 of the 52 World Championship Grands Prix he entered, a winning rate of 46.15% — the highest in Formula One history. He took 29 pole positions (55.77% of entries), 23 fastest laps, and 35 podium finishes at the time of his retirement. His record of five championships was equalled by Michael Schumacher in 2003, and later by Lewis Hamilton in 2018.
On 23 February 1958, two members of Fidel Castro's 26th of July Movement kidnapped Fangio from his hotel in Havana on the eve of the Cuban Grand Prix, aiming to embarrass the Batista government by disrupting the race. Fangio was held for 29 hours, allowed to listen to the race on radio, and released unharmed after being treated courteously by his captors. He later described it as "one more adventure."
After retirement, Fangio remained a prominent figure in motorsport and in Argentine public life. He served as honorary president of Mercedes-Benz Argentina from 1987. He formed a lasting friendship with Ayrton Senna, whom he described as "my heir and successor" after Senna's death at Imola in 1994. Fangio died on 17 July 1995 in Buenos Aires from bronchopneumonia and kidney failure, aged 84. His pallbearers included Stirling Moss, Jackie Stewart, José Froilán González, and Carlos Reutemann.
The Juan Manuel Fangio Museo was inaugurated in his birthplace of Balcarce in 1986 and houses his trophies and cars, including the Mercedes-Benz W196. Six statues of Fangio, sculpted by Catalan artist Joaquim Ros Sabaté, stand at circuits and locations including Monaco, the Nürburgring, Monza, and Buenos Aires. A W196 driven by Fangio during his 1954–55 championship seasons sold for $30 million at auction in 2013. He is consistently ranked among the greatest Formula One drivers of all time by statistical analyses, and the Australian English slang phrase "fang it" — meaning to drive at high speed — is derived from his name.