Here is how Twitter reacted to the world number's triumph.
Caroline Wozniacki, a close friend of Serena Williams, was one of the first on Saturday to congratulate the American on her latest success.
Wozniacki, who bowed out of the grand slam in the second round, wrote: "Big congratulations to my big sis @serenawilliams on #19! Such an inspiration! #champ"
Hall of Famer, former world number one and 16-time grand slam champion Billie Jean King was another prominent tennis icon to send her best to her fellow American.
"Congrats on your @AustralianOpen win @serenawilliams. You're a true champion for our sport have raised the bar once again! #19andcounting," tweeted King, who won the 1968 Australian Open.
Countrywoman Varvara Lepchenko, who was eliminated in the third round, joined the growing chorus of congratulators.
"Congrates to @serenawilliams on her 19th GS!!!What an inspiration!!!" Lepchenko posted.
Journalists from across the globe also congratulated Williams.
Daily Mail reporter Riath Al-Samarrai said: "Serena Williams is 33 and still doing this to people."
Craig O'Shannessy, a lead analyst for the WTA, wrote: "The serve was incredible tonight. #serena wins 6-3 7-6(5) over #sharapova. It answered every single question. #ausopen great match ladies!"
New York Times writer Ben Rothenberg, meanwhile, revealed an interesting insight into Williams.
"One Serena winning tradition? Chicken. She sent #AusOpen staff out to get her some from chain Red Rooster. Also feasted on chicken at USO14," Rothenbeg wrote.
While Williams earned top honours at Melbourne Park, there was still plenty of recognition for the beaten Maria Sharapova.
Australian Olympic and Commonwealth Games gold medalist Giaan Rooney was impressed by the Russian's character following the match on centre court.
"One of the best 'runner-up' acceptance speeches I have heard. Nicely played #Sharapova #AusOpen," Rooney said.