"From what we saw, it looks like congressman Akbar was the target of the attack," Geary Barias, Manila's police chief, told local radio.
The driver of another legislator was also killed and around eight people, including at least two lawmakers, were injured in the blast which tore the roof off the southern entrance of the congress.
Jose De Venecia, the house speaker, said he had ordered a "clean sweep" of the sprawling complex, located north of the capital Manila, to ensure "there are no other bombs that are left behind".
Joel Villanueva, a congressman, said less than 50 of the house's 275 members were inside when the bomb exploded.
"It was a very huge explosion," Villanueva said. "We are stunned."
Al Jazeera's Marga Ortigas, reporting from the capital Manila, said the police have set up checkpoints in many surrounding areas following the blast.
She said: "A hearing to discuss Gloria Macapagal Arroyo's [the president] possible impeachment was meant to be held today, and the blast may have been used as a distraction."
Last month, a blast tore through a shopping mall in Manila's financial district, leaving 11 people dead and injuring over 100.
Police initially thought a bomb was to blame, but later said the explosion was an industrial accident.
Tuesday's blast occurred amid heightened political tensions in the country.
Arroyo was set to face a third impeachment hearing in as many years amid a barrage of political storms and corruption scandals in the country.