The win not only broke his own record for number of medals – taking his total Olympic medal tally to 20 – but it also made him the first man to defend an Olympic swimming title twice, after previously taking the title for this event in Athens and Beijing.
A delighted Phelps said after the momentous win: “To win a gold medal and be the first to three successive titles is something pretty special and something I'm pretty happy for.”
The 27-year-old had already made history on Tuesday evening at the London 2012 Olympic Games, when he became the most decorated Olympian of all time.
Phelps won the 18th and 19th Olympic medals of his career to pass Russian gymnast Larisa Latynina’s tally of 18, which had stood since 1964.
The evening began with Phelps winning silver in the 200m butterfly before claiming gold in the 4x200m freestyle relay alongside USA team-mates Ricky Berens, David Walters and Ryan Lochte.
“It's very special,” said Phelps afterwards.
“There are still other races and that is what is on my mind right now. I am going to attempt to sleep. I am not sure if it is going to be possible."
Phelps had looked set to win the 200m butterfly for the third successive Games, but was beaten to the wall in the closing stages by South Africa’s Youth Olympic champion Chad le Clos, who finished strongly to pip the American by just five hundredths of a second.
After anchoring the USA to gold in the relay, however, Phelps ensured that his name was etched into the record books once again, having won more Olympic medals than any other athlete in history, with IOC President Jacques Rogge praising the American’s accomplishments.
“To take part in an Olympic Games is an achievement for any athlete - to win a medal makes you a member of an elite band; but Michael Phelps has made Olympic history tonight by winning his 19th medal and I salute his unique achievement,” said IOC President Jacques Rogge. “He breaks the record of Russian gymnast Larisa Latynina and in doing so he joins a group of athletes who have continued to strive for excellence in sport.”
Phelps made his Olympic debut as a 15-year-old at the Sydney 2000 Games and won his first medals four years later in Athens, when he won an incredible six gold medals and two bronzes.
The American surpassed that achievement in Beijing in 2008, however, when he broke compatriot Mark Spitz’s record of seven golds at a single Games by winning all eight events that he entered, breaking seven world records in the process.
Watch his performance in Beijing 2008