The move is part of a consolidation of the company's advertising into Fallon, which already handles the remainder of its above-the-line business.
Fallon recently launched a new £30m brand campaign based on the theme 'Together We Can Do More'.
Justin Billingsley, Orange's UK brand director, told Brand Republic, the thinking behind the appointment of Fallon is to unite all of Orange's communications under one brand idea: "Unfortunately it comes at the expense of Mother, it was a difficult decision, but is not an indication of Mother's performance on the 'Gold Spot' campaign."
Billingsley said that he hoped cinemagoers "wouldn't notice" when Fallon's first 'Gold Spot' ad launches in February 2009.
Two more Gold Spot ads created by Mother will launch before the end of this year as the account switches to Fallon.
Mother retained the Gold Spot business in September 2006 following a pitch against Fallon, which handles the brand's pan-European business.
The agency's Gold Spot ads have included appearances from Snoop Dog, Steven Seagal, Darth Vader and John Cleese. 'West Wing' star Lowe appears in the most recent.
Billingsley is currently appearing in the latest BrandRepublic.tv interview, in which he and Fallon's Magnus Djaba take questions from Brand Republic community members on Orange's new brand positioning.