Jimmy Wilde's birth certificate shows he was born in Craig Berthlwyd (Pentwyn Deintyr) (now known as the Graig), Quakers Yard, Merthyr Tydfil but his parents later moved to the village of Tylorstown in the Rhondda Valley when Wilde was twelve years old. Wilde was the son of a coal miner, who himself worked in the coal pits. Wilde was small enough to crawl through gullies impassable to most of his colleagues. Wilde first fought at the age of sixteen in fairground boxing booths, where crowds were amazed by his toughness and ability to knock down much larger opponents, most of which were local toughmen weighing around 200 lbs. In 1910 Wilde married his wife Elizabeth and was a father the same year. He left Tylorstown Colliery in 1913. In 1916 Wilde joined the army and was sent to Aldershot as a PT instructor.

The record books often show that Wilde started boxing professionally in 1911 but it is widely assumed that he had been fighting professionally for at least four years before that. Wilde's claim that he had at least 800 fights is probably greatly exaggerated, but it was rather more than the 144 shown in Boxrec and elsewhere. Wilde's officially listed debut was on 26 December 1910, when he fought Les Williams to a no-decision in three rounds. His first win came on 1 January 1911, when he knocked out Ted Roberts in the third round.

Wilde went undefeated in 103 bouts, all of which were held in Britain, a remarkable achievement. In the middle of that streak, on 31 December 1912, he won the British 7 stone championship by beating Billy Padden by an eighteenth-round knockout in Glasgow. He finally lost his undefeated record when he challenged Tancy Lee for the vacant British flyweight title and Europe championship on 15 January 1915 in London. Wilde was knocked out in the seventeenth round (of twenty).

Wilde then embarked on a sixteen-fight knockout streak, and on 14 February 1916, he won the British flyweight title by beating Joe Symonds by a knockout in round twelve at the National Sporting Club in London. On 24 April 1916 Wilde beat Johnny Rosner by a knockout in the eleventh round at Liverpool Stadium to win the IBU world flyweight title. On 13 May he had two fights on the same day at Woolwich Dockyard (against Darkey Saunders and Joe Magnus), winning both by knockout, both fights combined lasting less than five rounds. On 26 June Wilde returned to the National Sporting Club to take his revenge on Tancy Lee with an eleventh-round knockout. On 18 December Wilde became recognised as the first World Flyweight Champion (the IBU title was only recognised in Europe) when he defeated Young Zulu Kid of the United States whose seconds threw in the towel during the eleventh round of their bout at the Holborn Stadium.

In 1917, he retained the title by beating George Clarke by a knockout in four. With that win, he also won the European title and recovered the British title. But that would be his last title defence, as soon he decided to vacate the world title. He kept fighting and winning, and in 1919, he beat Joe Lynch, another boxer who was a world champion, by decision in 15. In 1920 he went undefeated in 10 fights, but then, he lost by a knockout in 17 to former world bantamweight champion Pete Herman, who outweighed Wilde by more than a stone (14 pounds), in 1921. The bout was originally scheduled as a title defence, but Herman had lost his championship to Lynch the month before. Herman easily regained the bantamweight title from Lynch in July 1921, leading some to suspect that he had left the title behind with Lynch in America intentionally. That was the fight that marked his return to Britain after touring the United States all of 1920. After a win over Young Jennings, he announced his retirement.

Wilde returned to the ring out of a sense of obligation to defend his title against Pancho Villa on 18 June 1923. After losing by a knockout in seven to the Philippines' first world champion, Wilde announced his retirement.

Jimmy Wilde lived the last few years of his life in the Cadoxton district of Barry, South Wales. With his final boxing winnings, Wilde entered into several business schemes, including a Welsh cinema chain, none was successful and he spent his final years in poverty. In 1965, Wilde suffered a serious mugging at a train station in Cardiff, from which he never recovered. His wife, Elizabeth, died in 1967, and two years later Wilde died in a hospital in Whitchurch. He was buried in Barry Cemetery.

He had a record of 137 wins, 4 losses, 2 draws and 8 no-decisions, with 100 wins by knockout, which makes him one of the most prolific knockout winners of all time, according to Ring Magazine, publication which also named him the 3rd greatest puncher of all time in 2003.

In 1990, Wilde was elected into the International Boxing Hall Of Fame as a member of that institution's original class. In 1992 he was also inducted into the Welsh Sports Hall of Fame and one of his prize winning belts is part of the organisation's display.