The polls come against the backdrop of heightened political tension since the approval in April of a divisive new constitution and a series of crackdowns on opposition protests.
Critics say it paves the way for President Faure Gnassingbe to further extend his family’s decades-long grip on power.
The president’s ruling Union for the Republic party, however, says the new system is more democratic and representative.
Over 4 million people are registered to vote in the polls which will give the opposition the chance to gain more seats in parliament.
Regional and municipal councillors will be responsible for electing senators, allowing the start of an upper house of parliament.
The exact number of senators is yet to be determined.
After boycotting the last election, opposition parties have been rallying their supporters to challenge the ruling party in the polls.