People.com was first to report Liddell's proposal to Northcott on Nov. 4 following a helicopter ride to the Grand Canyon.
Liddell, a father of two children, has never been married but was previously engaged two years ago.
Liddell's future in MMA remains uncertain following his knockout loss to Rich Franklin at UFC 115 in June, Liddell's third straight loss and fifth in his last six fights. At the post-fight press conference, UFC president and close friend Dana White stated, Liddell will "never fight in the UFC again."
Besides card-playing, Northcott also works for internet marketing company High Traffic Media.
In February, the two were taped for a viral Reebok campagin working out in the nude (except sneakers, of course).
According to People.com, the couple have been together for over a year.