The contract was won following a competitive pitch, and is effective today (1 December).
Edelman succeeds Lansons, which was appointed to run PR for Crimson Hexagon in January this year.
Crimson Hexagon has a built-in data library hosting more than 750 billion social posts, and works with brands including Legal & General, EE, O2, the Post Office and Saatchi & Saatchi and VML.
The firm was founded in Boston, Massachusetts in 2007.
