"There is every reason to congratulate David Cameron for having made historic changes (within his party) in a very short time," Reinfeldt, who heads Sweden's conservative Moderate party, told a press conference.
"We've been in touch over the past year and I'm looking forward to working with him," he added.
Reinfeldt said Cameron had inherited "Europe's most difficult task: that of putting British public finances in order."
"The Labour Party has left behind a budget that is deficit-plagued to levels equivalent to what we've seen in Greece," Reinfeldt said.
When asked about the eurosceptic stance of Cameron's Conservatives, Reinfeldt said that their unlikely coalition with the pro-European Liberal Democrats could signal policies more open to the European Union.
The Liberal Democrats "could create a counterweight," Reinfeldt said, "and give the government a more pro-European point of view."
Prior to his election in 2006, after 12 years of Social-Democratic rule in Sweden, Reinfeldt had worked on re-centering his conservative party.
He compared the Swedish centre-right's victory with Cameron's rise to power after the Blair-Brown era.
"It's amusing to notice there is a parallel between what happened in Sweden and what's happening right now in Britain, after 12 years of Labour rule," said Reinfeldt, who is running for reelection on September 19th.
Sweden's left-wing opposition has been far ahead of the government in many polls, but two recent surveys have signaled the gap between the two blocks might be narrowing.