The 28-year-old went straight into the Steelbacks team for last Friday's must-win clash with Worcestershire Royals, replacing West Indian Jason Holder. who has picked up an injury.
Holland will be available for the remainder of the County's Royal London Cup campaign, as well as next week's 50-over tour match with Pakistan.
"With three seamers down and an injury to Jason Holder we felt the need to add to our squad for the rest of our 50 over campaign." said Northants head coach David Ripley.
"Ian played against us in La Manga (in pre-season) and caught the eye, he's a three-dimensional cricketer perfect for 50 over cricket."
A middle-order batsman and fast medium bowler, Holland was born in the USA to a British father and an American mother, before heading to Australia when he was a toddler.
Holland has only limited experience of one day cricket, having played just two 50-over and one T20 game for Hampshire in his career so far.
Northants have lost three of their four Royal London matches to date, and against they made three changes to the team that lost to Lancashire on Wednesday for Friday's Worcestershire date.
Into the team came Holland, Nathan Buck and Ben Curran, replacing the injured Holder, Saif Zaib and Ricardo Vasconcelos respectively.