Ko, who was born in South Korea but has lived in New Zealand since she was six, made the announcement via her Twitter feed with a link to a Youtube video in which she appears with one of the country's top rugby players, Israel Dagg.
"Made a monumental decision today with a little help from my @AllBlacks friend @Izzy_Dagg #LOVEGolf," Ko tweeted.
All Blacks back Dagg spends the entire video, that lasts almost five mintues, asking Ko when she would make the decision.
"When are you going pro? I want to be the first one to know," Dagg asks, only for Ko to tell him she still has things to work on with her game.
Ko finally confirms the decision after making a long putt to 'beat' Dagg in their round.
"Okay I'll do it, turn pro," Ko says. "Right now, right this second. Definitely."
Ko added that she hoped to play her first tournament as a professional in Florida in mid-November.
The teenager has won four professional tournaments as an amateur and was runner-up in the fifth women's Major, the Evian Championship, last month.
Her mother said earlier this month that they had asked the LPGA tour to issue her an exemption for her to become a member.
The LPGA restricts the number of tournaments for players under 18.