McNamara admitted on Thursday he was looking for cover for left-sided defender Gavin Gunning, whose knee injury might keep him out for another month.
And he succeeded in signing 20-year-old Good on a deal until the end of the season.
The Australian-born player, who arrived at Newcastle from Melbourn Heart, goes straight into the squad for the Firhill trip.
McNamara said: "Curtis comes to us highly recommended and from a well-respected club.
"He is left-footed and can play as either a central defender or left-back. These are areas that require cover and it was important this was addressed during the window.
"He is 6ft 1in and strong and should give a different option to the defenders already at the club.
"I am very happy to have this deal completed - it offers Curtis the opportunity to get some game time whilst enhancing our squad for the latter part of the season."
Good, a graduate of the Australian Institute of Sport, joined Newcastle on a six-year contract in 2012.
He has captained the reserve side and made his first-team debut in a Capital One cup tie against Morecambe in August.
The Australia Under-23 international played in the final of the same competition the previous season during a loan spell with Bradford.