Five policemen and two children were among the victims of the attack in the city of Quetta.
There are fears the death toll could rise as many of the 35 people wounded are in a critical condition.
Terror group Islamic State has claimed responsibility for the explosion.
Hashim Ghilzai, an administration official in Quetta, said: “(The bomber) was trying to enter the polling station. When police tried to stop him he blew himself up.”
Source: Sky News