Yunus al-Ramah, head of the United Iraq party, had been hosting a social gathering at his home in the town of Al-Hadhr, in Nineveh province, when the attack took place, according to security and medical officials.
"The suicide bomber targeted people gathering in Ramah's garden," said police First Lieutenant Islam al-Juburi.
Five people were killed -- Ramah and four of his relatives -- and six others wounded, Juburi and a doctor said.
The attack comes ahead of Thursday's elections in Nineveh and Anbar, two Sunni-majority provinces where polls were delayed by officials who cited security concerns.
Also Read
Twelve other provinces held elections on April 20.
No group immediately claimed responsibility for the attack, but Sunni militants linked to Al-Qaeda have sought to intimidate candidates, particularly in a bid to derail elections in majority-Sunni areas of Iraq.
Nineveh province is one of Iraq's most violent, on a per capita basis, according to British NGO Iraq Body Count.
Analysts say a lack of effort by the Shiite-led authorities to address the underlying causes of the demonstrations has given militant groups fuel and room to manoeuvre to carry out their activities.
Political leaders have pledged to resolve outstanding disputes, and Prime Minister Maliki has met with two of his main rivals in a bid to ease tensions, but no tangible moves have been agreed.