Bangkokians will vote for their governor on May 22, the same date that voters in Pattaya will choose their councillors and mayor.
The Election Commission (EC) announced on Monday it had decided on the election date for the two cities.
The date will be officially declared on March 25.
Candidacy registration will take place from March 31 to April 4.
Incumbent Bangkok governor Aswin Kwanmuang said he would probably decide whether to seek a second term in two weeks.
Pol Gen Aswin said he would need to consult his family while making the decision.
"I've been thinking about (whether to run) every night," he said.
Meanwhile, Sakoltee Phattiyakul, who has joined the race after he stepped down as Bangkok deputy governor last Monday, said via Facebook that he would announce his election campaign policy on March 24.
Also, the main opposition Pheu Thai Party said it was ready to compete for the Bangkok city council seats across 50 constituencies.
Party leader, Dr Cholnan Srikaew, gave a strong indication earlier that the party would not field a candidate in the Bangkok governor race.
He said last month that the Pheu Thai would only enter the Bangkok governor race if it could send a better-qualified candidate than Mr Chadchart.
Dr Cholnan has said the party has yet to find someone who "ticks all the boxes".
In Pattaya, Mayor Sonthaya Kunplome is continuing to keep people guessing about his plans, saying only that he is ready for another run.
Culture Minister Itthiphol Kunplome said on Friday he expected his elder brother would stand for another term as he had plans to make Pattaya once again a holiday city, serving the Eastern Economic Corridor.