Juan Bautista Idiarte Borda y Soumastre (April 20, 1844 – August 25, 1897) was the 17th President of Uruguay.

Originating from the Uruguayan department of Soriano, which he was to represent in Uruguay's chamber of deputies, Idiarte was a member of the Colorado Party, which dominated the country's politics for many years.

On March 21, 1894 Duncan Stewart, interim President of Uruguay stepped down, and Idiarte replaced him in that office.

Idiarte's presidency was beset by a number of severe difficulties which found their origins in a host of commercial, ideological and personality issues, in the background of Uruguay's intermittent Civil War.

Subsequently, the reputation of Idiarte was greatly overshadowed by that of José Batlle y Ordóñez, who later became a long-serving President.