Southeard, who takes up her role on Monday, is tasked with speeding up the development and integration of Lanson’s digital content and social media work.
Southeard spent the intervening period building its multi-channel offer, which later became known as Engage.
Earlier in her career, she was managing director of TNR Communications, a specialist content agency owned by the Press Association.
All eight of Lansons’ digital, social media, content and design staff will report to Southeard and she will begin her work by reviewing the agency’s offer and presentation to clients.
Tony Langham, chief executive of Lansons, said: "We are absolutely delighted to announce that Claire is joining us. We see this investment and Claire joining as fundamental to our future success."
Bell Pottinger went into administration last month after news of controversial client work and its subsequent expulsion from the PRCA hit national headlines.