Danson, who takes up his position with immediate effect, currently holds 28.78% of the ordinary share capital of TMN.
He first emerged on the shareholder register in March when TMN received a 50p per share offer from Tangent Communications -- an offer which was subsequently withdrawn.
Danson started Datamonitor in 1990 and sold it on to Informa in 2007 for £502m. According to the Daily Telegraph, Danson made a total of £165m from the business.
In April this year, he bought a 50% share in left-wing weekly magazine New Statesman from Labour MP Geoffrey Robinson, who retained 50%.
Danson also holds directorships at Estel Property Investments and Progressive Capital.
Peter Harkness, chairman of TMN, said: "[Mike] has a tremendous track record in developing media companies and brings extensive relevant expertise and experience to the group."
TMN Group companies include full service digital advertising agency EDR, online market research arm ID Factor, and research analysis agency ICD Research.