The former campaign strategist Alberto Fernández won nearly half the vote.
Argentina financial crisis
The Argentine peso has fallen more than half a percent today, with roughly 60 pesos to the US dollar.
In an effort to boost the peso, the country's Central Bank has said they will sell US dollars to the tune of $800m (£624m).
Argentines will go to the polls this Sunday with a swing to the left and change of government predicted.
Before a blackout period began this morning, current centre-right President Mauricio Macri finished his campaign in Cordoba.
He has presided over a period of serious economic crisis in the South American country with polls placing opposition leader Alberto Fernandez 20% higher.