The Haitian-Japanese star defeated Czech player Petra Kvitova 7-6 (7-2), 5-7, 6-4 on Saturday in Melbourne.
"Thank you, everyone," Osaka said following her match. "I am really honored to have played in this final."
The victory earned Osaka her second grand slam championship. In September, she defeated Serena Williams in a controversial match.
“Definitely she is a great one,” said Kvitova, who’s a two-time grand slam champion herseld.
She is the first player from Japan to hold the No. 1 ranking, writes Quartz.