The 15-minute debate focused on two topics: jobs and welfare.
Stefan Löven, the former head of blue-collar union LO, attacked the prime miinister for not doing enough to tackle unemployment.
"You need to face the fact that unemployment is higher now than when yyou came into power, long-term unemployment is higher and youth unemployment is higher. Nevertheless, you stand there and seem rather satisfied."
Reinfeldt, who is head of the ruling conservative Moderate Party, countered by questioning Löfven's statistics: "I haven't read those reports, they don't support what Mr. Löfven is saying. Reports do say that being able to keep more of your paycheck creates more jobs. That is perhaps the most effective way of creating jobs out there."
The government, which has been making public parts of its budget on a piecemeal basis, will present its full budget proposal on Wedneday. Similarly, the Social Democrats, the main opposition party, has yet to present its shadow budget.
This was the first time that the party leaders from Sweden's two biggest parties have met in a debate. Löfven is not an MP, and so cannot speak for his party in parliament. He became leader of the Social Democrats in January last year.