A delegation of 50 lawmakers – which would have the power to replace parliament in the event of the threat of war or an outright conflict – held the drill on Monday at an unknown location, said speaker Urban Ahlin, declining to give details on what the manoeuvre involved.
"These are secret scenarios… you were exposed to pressure," Ahlin told AFP on Tuesday. "It went really well."
The delegation is made up of politicians from the left-wing, right-wing and far-right parties.
A non-Nato member, Sweden has not seen armed conflict on its territory in two centuries.
The drill has been planned since 2014, but Ahlin said an increasingly hostile situation in the world and in the region also prompted the exercise.
"The worsened (global) environment also has a significance," he said, adding that the drill would have been postponed if Sweden deemed the world and region safe.
The last time lawmakers held such an exercise was in 1997.
"If everything had been great then people would have said we can wait for a few more years," Ahlin said.
"Unfortunately, we see a direction in which countries are boosting their weaponry," he added, without naming any countries.
Sweden this month announced plans to bring back conscription this year – seven years after abandoning it – to respond to global security challenges including Russia's assertive behaviour in the Baltic Sea region.
"We are in a context where Russia has annexed Crimea," Swedish Defence Minister Peter Hultqvist said at the time of the announcement, adding: "They are doing more exercises in our immediate vicinity."
The Swedish military's budget has been slashed over the past two decades as its mission was revamped to focus more on peacekeeping operations abroad and less on domestic defence.
Russia has repeatedly warned Sweden and neighbouring Finland against joining Nato, an issue regularly debated in both countries.