The 11-year-old agency will be renamed Publicis Modem Korea, the digital arm of Publicis Worldwide, which currently does not have an office in South Korea.
Portfolio will join Publicis Modem's other offices in Asia which are located in Beijing, Hong Kong, Kuala Lumpur, Singapore, Taiwan and New Delhi.
Founded in 1998, Portfolio provides web development, marketing, online advertising, search, database marketing and tracking and search engine optimisation services.
Its clients include prominent Korean and international brands such as Microsoft Korea, Prudential, Marriott International, Nissan Korea, Estee Lauder, Woonjgin Group, Epson, Choongwae Pharmaceutical Corp, Yuhan Kimberly and Nongsim Kellogg.
Heewoon Park, founder and CEO of Portfolio, will remain at the head of the agency.
Park said: "Publicis Groupe gives us the international scale we've been looking for in order to best meet our clients' needs in this increasingly globalised world. Right from the beginning, we felt a very powerful fit with Publicis Modem.
"This is exciting news for everyone at Portfolio, and we look forward to benefiting from the added expertise, further scale, and global reach associated with this digital powerhouse."
Digital advertising in Korea is a thriving market. According to ZenithOptimedia, internet adspend grew nearly 40% in 2007 to take a 13.7% share of total adspend of nearly $10bn. By the end of 2007, there were 14.8m broadband subscribers representing 78% of Korean households.
Publicis Groupe is already present in Korea through Publicis Welcomm and Publicis Dialog, Leo Burnett, Publicis Events Worldwide (Emotion), Saatchi & Saatchi and Starcom MediaVest Group (SC Seoul).
Martin Reidy, CEO of Publicis Modem, said: "Asia is a critical market for Publicis Modem and a key part of our global expansion. We were committed to finding a group with the passion, creative innovation and technical acumen synonymous with the Publicis Modem brand.
"The team at Portfolio fit the bill exactly. With the explosive growth in the region, this acquisition is an incredible opportunity for everyone involved."
Arlene Ang, regional managing director of Publicis Modem, said: "The acquisition of Portfolio gives Publicis Modem access to the Korean market, one of the world's fastest growing markets in digital advertising and communications. It also complements our successful start up of network offices in Hong Kong, Beijing, Taiwan, New Delhi, Kuala Lumpur and Singapore."
The acquisition follows the launch by Publicis Groupe of a new digital division named Vivaki, headed by Jack Klues and David Kenny. The new unit will take advantage of the scale and knowledge of group agencies including Digitas, Starcom MediaVest and ZenithOptimedia to develop new services for clients.