At 61 polling stations around the country, voters will be able to exercise their democratic mandate early, having their ballots put into secure storage and added to the count with all the others on Saturday.
Polls opened at 1700 local time, staying open until 2000.
On Thursday, the same selected polling stations will be open in the morning from 0900-1200 and again on Friday from 1000-1600.
On the main polling day on Saturday, more than 1,000 polling stations in Latvia and overseas will be open from 0700-2000.
The Central Election Commission (CVK) tweeted a reminder to voters.