In the midst of double-digit inflation and a stagnant economy, Argentines on Sunday handed victory in the presidential runoff election to 56-year-old Buenos Aires Mayor Mauricio Macri of the Cambiemos (Let’s Change) coalition.

With 76% of the vote counted as we went to press, Mr. Macri led with 52.87% against 47.13% for President Cristina Kirchner’s Peronist Front for Victory (FPV) candidate, Daniel Scioli.

The...