The group confirmed to PRWeek that Chadlington, who has latterly held the role of senior client adviser at Huntsworth, left the company on 5 April.
The Conservative peer announced his intention to stand down as chief executive of Huntsworth in 2014, having held the CEO role since 2000, but remained in an advisory capacity after Taaffe arrived in April 2015.
A known confidant of Prime Minister David Cameron, Chadlington made his name with Shandwick – the predecessor to Weber Shandwick – which he founded in 1974 and built to become a global powerhouse before selling to The Interpublic Group in 1996. He was made a Conservative peer the same year.
He remained chairman of Shandwick until becoming CEO of Huntsworth shortly after buying a 29.9 per cent stake in the group, which he built to number more than 70 offices worldwide.
Huntsworth has undergone a tumultuous period in recent years, with the departure of Chadlington and chairman Lord Myners alongside poor trading results. Chadlington saw his annual remuneration fall 29.5 per cent in 2014 after bonus payments to executive directors were scrapped because none of their financial targets were met.
However, there have been signs of recovery since then, with some "marginal" revenue growth in 2015, led by Huntsworth Health and Red. Grayling and Citigate remained in decline.
According to the register of interests on Parliament’s website, Chadlington’s advisory role at Huntsworth saw him working with clients including Associated British Foods, The Carlyle Group, the London Stock Exchange, Serco Group, the Singapore government, 3M and Gatwick Airport.
Separately, Chadlington has worked with business intelligence group GPW and private equity firm KRG via his vehicle Chadlington Consultancy.