Sir Martin, the founder and former boss of advertising giant WPP, said the deal was an “important second strategic step” for S4 Capital as it looks to target the west coast of America and technology giants.
The acquisition of San Francisco-based MightyHive, which specialises
in programmatic marketing, is the second takeover by Sir Martin since he left WPP in April, following allegations of misconduct and that he misused company funds.
His new venture has already triumphed against WPP in a high-profile battle to buy Dutch firm MediaMonks, which also recently opened an office in San Francisco.
But Sir Martin has previously said S4 Capital would not compete head to head with WPP, and claimed his new company was a “peanut” in comparison.
Announcing the cash-and-shares deal with MightyHive, which is structured as a merger, Sir Martin said: “The peanut has now morphed into a coconut, and is growing and ripening.”
S4 floated capital in September, raising £51 million including a £40 million investment by Sir Martin.
Following his departure earlier this year, WPP carried out an inquiry into allegations that Sir Martin misused company funds, but details of the investigation were never disclosed.
It has been claimed that the probe looked into whether he used company cash to pay for a sex worker, allegations that Sir Martin has “strenuously” denied.