BUENOS AIRES — President Mauricio Macri of Argentina on Monday hailed his party’s strong showing in midterm elections as a mandate to press forward with a controversial package of labor, tax and pension reforms that he says will put the country on a path toward sustained economic growth.

“We have entered into a period of permanent reform,” Mr. Macri said, smiling broadly at an early morning news conference. “Argentina must not stop and must not fear reforms, because to reform is to grow, progress, evolve.”

Mr. Macri’s alliance — Cambiemos, or Let’s Change — exceeded analysts’ projections for Sunday’s vote, becoming the first party since 1985 to win in Argentina’s five largest electoral districts. It picked up nine seats in the Senate and 21 in the lower house of Congress, bolstering its count in the legislature, though Cambiemos remains a minority bloc.

Former President Cristina Fernández de Kirchner, the standard-bearer of the Peronist Party, won a Senate seat. That will give her a formal platform to continue fighting Mr. Macri’s policies, which Mrs. Kirchner says benefit the wealthy at the expense of the poor. The office will also probably shield her from prison if she is convicted of pending corruption charges.