Established in Germany in 2008, Wildcard has revenues of €1.5m (£1.35m) and its clients include BMW, EA Games, and Bosch. Founder Georg Reckenthaler will remain with the business under its new ownership, serving as managing director.
Reckenthaler said: "By joining Ranieri and combining our talented teams, we are not only able to further deliver unique and creative campaigns for our clients but also extend the scope and depth of industry relations into Europe and beyond."
Ranieri, which was founded in 2002 by Pietro Ranieri, has 18 staff, and clients include Asus, as well as audio products businesses JBL and AfterShokz.
The deal follows Ranieri's acquisition of eight-strong French tech agency Reflexion Publique in May.
The agency's founder said: "Ranieri is currently rolling out a three-year plan to grow its service offering as well as geographies by continuing to acquire first-class agencies such as Wildcard. By bringing Wildcard into our growing network, we unlock additional shared value through our complementary service offering, sector focus and increased geographical reach."
Ranieri's parent company Vodrum was itself acquired by The Marketing Group in 2016 for a total of €13.7m (£11.6m).