Some arrived at the embassy hours before it opened and many took a day off work to cast their votes during office hours.
Myanmar expats in Singapore have until October 18 to vote.
More than 34,000 expats applied to vote, including more than 20,000 in Singapore.
On Thursday, expats in Malaysia and South Korea also cast their votes.
Thar Phyo in Singapore said: “I lived in Tamwe and cast three votes in advance. In my view, the embassy does its best but it is not done systematically so it takes a long time.”
Some migrants criticised the time it took to vote.
Ei Wai said: “It was difficult to find my name on the voter list. The space in the embassy was narrow and there wasn’t many staff to help the voters at the embassy. They tried their best.”
Long queues had built up by noon on Thursday with well-wishers offering bottled water under the hot sun.
Some were denied the chance to vote despite applying for an advance ballot.
Kaung Mon Myint said: “Our whole ward in Mayangon Township is not included in the voter list announced by the embassy so we cannot vote. I applied but our names have not appeared. Wards two, three and five are included but not ward four.”
On average 200 people could vote in an hour and some were worried that they miss out, said Ant Htoo Naing.
Nationals can vote in 44 embassies and consular offices in 37 countries.
While advance voting was criticised after the 2010 general election, the same process was seen as non-corrupt at the 2012 by-elections.