The couple's chosen day big day also marks the sixth anniversary of the infamous police raid on the Coatesville mansion Dotcom once called home.
Dotcom wanted to marry on January 20 to turn the significant day into "a day of joy".
The pair first went public with their relationship two years ago and they moved to Queenstown six months ago.
Liz is said to be very close with Dotcom's children from his former marriage to Mona Dotcom.
Dotcom told NZME today's celebration would be "a small private ceremony".
Earlier this month he posted a photo of his extended family, including his five children from his previous marriage to Mona Dotcom.
On this day six years ago Dotcom was arrested when the anti-terrorism Special Tactics Group raided the $30 million Coatesville mansion he was renting.
The raid was part of a worldwide FBI operation to shut down the Megaupload file-sharing website, which was allegedly part of a huge criminal copyright infringement operation.
Dotcom and Donnelly, who is 21 years his junior, began dating almost two years ago.
He blamed the US Justice Department for the collapse of his previous marriage.
