The deal sees Contempora joint founders and CEOs Francesco Conti and Giorgio Carrion join the H&K Italy board. Contempora's six other staff have also moved across to H&K.
H&K vice-president marketing EMEA Dominic Shales said the move was in response to a 'clear increase in client demand' for PA work in Italy.
Contempora - which mainly works in the healthcare sector - has clients such as Novartis, Schering-Plough, the regional government of Legnano and Milan's Luigi Sacco hospital.
The Contempora brand will be scrapped as a result of the takeover.
In 2000, H&K Italy - led by CEO and president Cesare Valli - bought environmental and CSR comms firm Gaia and last year it set up Digital PR, as a standalone interactive comms company.