The Senate approved the measure on a 40-0 vote Tuesday.
The House passed the bill last week. It goes to Gov. Sam Brownback and he is expected to sign it.
The measure arose from congressman Mike Pompeo’s nomination by President-elect Donald Trump as Central Intelligence Agency director.
If Pompeo is confirmed, the 4th District in south-central Kansas would have the state’s first special congressional election since 1950.
State law says a special election must occur from 45 to 60 days after the governor declares a vacancy. The bill would make the window from 75 to 90 days to give people overseas more time to return ballots.