LLYC - previously known as Llorente & Cuenca - joins as an associate partner on 1 July, more than doubling the total headcount of the global network.
It becomes the third agency to join in associate partner status, following French consultancy Image Sept and Fogel & Partners in the Nordic region last year.
The move has no impact on the ownership or leadership structure of LLYC, which will continue to be owned by its partners and operate under its own brand name and identity.
The partnership said the deal will give LLYC clients access to a network of more than 500 comms professionals across 16 offices, including New York, London, Frankfurt, Brussels, Berlin, Washington, Hong Kong and Beijing.
In turn, the global partnership’s clients will gain access to comms services in Spain, Portugal and Latin America, including offices in Madrid, Barcelona, Sao Paulo, Rio de Janeiro, Lima, Mexico City and Santiago.
Dirk von Manikowsky, partner at Hering Schuppener, told PRWeek the network agencies have set up practice groups for specific tasks, undertake knowledge-sharing and operate interships across different countries. "It's a very close partnership that allows us to have a seamless offering to clients," he stated.
"What time has taught us is, it's good to take your time and work on collaboration, integration, networking between the partners, and then partnerships comes to life."
LLYC, which generated global revenue of $45.3m in 2018, was a member of the AMO network until May this year. The agency previously worked with Hering Schuppener when the Germany-headquartered business was part of AMO.
LLYC was founded in 1995 by Jose Antonio Llorente and Olga Cuenca, It operates a range of services including financial comms, crisis and issues management, media and investor relations, corporate positioning and public affairs.
Asked about the reason to move away from AMO and join the WPP partnership, LLYC said: "We ended our partnership with the AMO network in May of this year because we understood that our international strategy needed a new focus. Finsbury offers us a strong US/Europe network, together with Middle East and Asia."
Jose Antonio Llorente, founding partner and president of LLYC, said: "I am thrilled that LLYC is joining this global partnership as it means giving our clients access to the best communication players in the world’s financial centres and political capitals.
"This partnership advances our strategy of combining a local focus with global reach, working with talented communications advisors all over the world."
Alexander Geiser, managing partner of Hering Schuppener and member of the Global Board of the partnership, said: "LLYC is the ideal match for our global partnership, as it complements both our offering in Europe and in the Americas.
"We look back on nearly two decades of cooperating with LLYC and their unrivalled offering in the Spanish- and Portuguese-speaking markets. We look forward to opening that potential to our multinational clients and to serve LLYC’s clients around the world."
Finsbury and Hering Schuppener initially launched the alliance in 2016, with Glover Park Group coming on board the following year. The group is currently working on around 60 joint projects across the world.
Last month, the Financial Times reported that Finsbury founder and chairman Roland Rudd had approached WPP about a possible MBO, according to "people familiar with the matter".