Teufelberger and Ryan have run the company together since PartyGaming merged with Bwin in March 2011 to create the world’s largest listed online gaming group.
Ryan is only 51 but has a family and wants to return to Canada after living in Gibraltar, where the company is based, for several years.
He will be paid a year’s salary of €573,000 (£465,000) when he leaves on 15 January, in line with his one-year rolling contract.
Teufelberger, an Austrian, joined Bwin in 1999, having previously worked for a decade in the gaming industry.
Since the merger, the firm has launched business across Europe, inked a partnership with social gaming group Zynga and re-examined an entrance to the heavily-regulated US market.
“The transition to regulated markets is continuing and we are entering a period of intense product and technology innovation that will now be led by Norbert Teufelberger, whose experience, as one of the pioneers in online gaming, is probably unrivalled,” said Simon Duffy, non-executive chairman of Bwin.party.
Teufelberger hit the headlines last month when he was questioned by the Belgian authorities in a dispute over licences.
Bwin is expected to report a slight fall in revenues in a trading update next week, as regulatory crackdowns in several countries hamper sales.