Tadini was born into a family of prosperous retailers. His father, Ercole Tadini, owned the Grandi Magazzini Italiani Tadini, a well-established chain of clothing department stores that operated across northern Italy. At the age of fifteen, Mario moved to Bologna to manage the family's store there, beginning a business career that would run in parallel with his passion for motor racing throughout his life.
Tadini's earliest recorded race was at the Giro delle Tre Province in 1929. That same October, he became one of the principal financial backers of a new racing outfit being assembled by Enzo Ferrari, contributing substantially to its foundation. He was named the first chairman of Scuderia Ferrari — a role that recognised his importance as a patron and early believer in the venture. By 1932, Tadini had sold his personal stake in the team, but he continued to race in Ferrari-entered Alfa Romeos throughout the remainder of the decade.
Tadini's greatest competitive successes came not on circuits but on mountain passes. He specialised in hillclimbing and became synonymous with the Corsa dello Stelvio, the annual race up the Stelvio Pass in the Alps. He won the event five consecutive times, from 1933 through 1937, earning the nickname Il Re dello Stelvio — the King of the Stelvio. The title was more than a tribute to his consistency; it reflected genuine mastery of a demanding and dangerous discipline.
His hillclimb record extended beyond the Stelvio. In 1935, driving an Alfa Romeo P3, Tadini won the prestigious Grossglockner Grand Prix in Austria, beating Richard Seaman in his E.R.A. into second place — a result that put him ahead of a driver who would go on to win a Grand Prix for Mercedes-Benz.
On the road, Tadini's finest result was a runner-up finish at the 1935 Mille Miglia. The previous year, in 1934, he had demonstrated remarkable pace: driving a Ferrari-entered Alfa Romeo Monza, his stage times between Brescia and Rome were faster than those of Tazio Nuvolari and Achille Varzi, who ultimately finished first and second overall. That Tadini did not convert that raw pace into an outright victory illustrated the difference between consistent speed and race management over the full Mille Miglia distance.
In the more demanding world of Grand Prix racing, Tadini's results were limited. His Championship-level appearances were confined to three events: the 1931 Italian Grand Prix, the 1934 Italian Grand Prix, and the 1936 Monaco Grand Prix. He finished none of them.
The 1936 Monaco race produced one of the more unfortunate incidents of his career. Tadini was swapped into a car previously driven by Nino Farina, which was leaking oil. The borrowed machine lasted a single lap before depositing oil at the chicane, triggering a significant pile-up. Among his other notable appearances, Tadini managed a sixth-place finish at the 1936 Tripoli Grand Prix and seventh at the 1930 Rome Grand Prix. His best national Grand Prix result was fourth at the inaugural Hungarian Grand Prix in 1936.
Tadini continued racing intermittently for many years after the Second World War, eventually making his last significant appearance at the 1953 Mille Miglia, where he retired. In an unusual choice for a driver of his background and era, he drove a Jaguar C-Type that he had purchased that April — a late flourish of sporting independence from a man who had spent most of his career in Italian machinery.
Tadini married twice. His first wife, Pierina, died in 1955; together they had two sons and a daughter. He had two further sons with his second wife, Marion. During the Second World War, he spent the conflict years at Lesa on the shore of Lake Maggiore.
Mario Tadini died on 22 August 1983 at the age of seventy-seven. His legacy rests on two foundations: his role as one of the earliest financial supporters of Scuderia Ferrari at a time when the team's future was far from assured, and his unmatched dominance of the Stelvio hillclimb, which gave Italian motorsport one of its most evocative regional champions of the interwar period.