The rugby star's 35th birthday was the same day.
The couple made public their engagement on McCaw's Facebook page last night.
More than 6000 wellwishers the world over have posted comments to his page congratulating the pair on their pending nuptials.
In a post on the All Blacks Facebook page New Zealand Rugby has reposted the official engagement snap of McCaw and Gemma Flynn with a short message celebrating the "great news".
"In case you missed it - he's off the market! In some great news from the holiday break Richie McCaw got engaged to his partner Gemma Flynn. Congratulations Richie and Gemma!"
In announcing the engagement, McCaw hinted the proposal was timed around January 1.
McCaw posted: "Happy new year to everyone. I've had a fantastic start to 2016 and feel very lucky. Gemma said 'yes'! It's been great celebrating our engagement with friends and family in sunny central Otago."