Everyone Was a Debutant in 1930
The 1930 World Cup, held in Uruguay, was the first ever staged. Thirteen teams accepted FIFA's invitation, and every one of them was making its World Cup debut by definition — there had been no earlier tournaments to qualify for or learn from. So the question of "who reached a final on debut" has a clean, neat answer at the very start of the story: in 1930, the two teams in the final, Uruguay and Argentina, were both first-time World Cup teams. They had no choice but to be debutants. The format itself made it so.
Argentina's Run to the First Final
Argentina were one of the strongest South American teams of the era. They had reached the final of the Olympic football tournament in 1928 — the unofficial world championship before the World Cup existed — losing to Uruguay there. In 1930, they came to the new tournament as serious contenders. Through the group stage and the knockout rounds, they played their way to the final, where they would once again face Uruguay. The match was a re-run of the 1928 Olympic final, with the World Cup trophy at stake instead.
A Final Decided in Montevideo
The 1930 final was played at the Estadio Centenario in Montevideo. Argentina led 2–1 at half-time, but Uruguay scored three times in the second half to win 4–2 in front of a packed home crowd. The host country lifted the trophy and became the first ever World Cup champions. Argentina, in their debut World Cup, ended as runners-up — the first nation ever to reach a World Cup final and lose it. Their long wait for a first World Cup title would last until 1978.
A Special Kind of Record
Reaching a World Cup final on your debut is, in pure record terms, no longer something a country can do — every team that has come along since 1930 has had earlier tournaments to play in first, and a country only counts as a debutant once. Argentina hold a particular kind of place in the record book: their first World Cup was the first World Cup, and they took it all the way to the final. The closest later equivalents are debut teams that surprised on their first appearance, but none have matched Argentina's 1930 path to the final itself.
Source
This article was written using information from Wikipedia.