Incumbent Porter Novelli and fellow preferred agency Burson-Marsteller lost out in the pitch.
The work will be handled by H&K's Mexican operations, headed by executive vice-president Manuel Juarez.
He said: 'This is a large (fee) for us and we will be expanding our team to serve the account more adequately.'
He said H&K will double the HP account team to six.
Countries in the brief include Agentina, Brazil, Chile, Colombia, Venezuela, Peru and Central America.
The account will not include work in Mexico, which will continue to be handled by PN.
The H&K team will report to HP Latin America head of communications Samuel Araiza.