The General Election is on Sunday 23rd December which will be a public holiday as is 24th December ( yes Christmas Eve! ) to allow people to travel back from their homes where they have to go to vote ( Shades of Mary and Joseph having to go to Bethlehem ). All government offices, banks, embassy services, and bars will be closed.

ATMs will be working. If you need to cash any travel checks, do it in plenty of time. Presumably the banks at the airports will be open.

IF - and it's a BIG IF - things go as usual - bars will close at midnight on Saturday 22nd and probably re-open OK on Sunday 23rd. On the Monday 24th banks and govt offices will closed and probably Embassies.

After the astonishing situation in Pattaya of the King's Birthday closures by the Police in contravention of the request that they be open by The Palace and after they were open last year on H M's birthday anything can happen
My thoughts are that:

21st and 22nd: buses, planes and trains will be very busy with Thais going home to vote. Expect bars to close early on 22nd.
Stock up with cash to cover the next couple of days. With the Christmas rush ATM's can run out of cash. Small shops and market stalls may close.

23rd Election Day, Banks and Govt Offices closed but shops and restaurants open. Bars should be open as usual in the evening as the polls finish at 5 p.m.

24th Public Holiday, Banks and Govt offices closed and probably Embassies. Transports will be very busy with the Christmas rush and Thais returning to work after voting.

25th Christmas Day is not a holiday in Thailand and things should be open as usual but many Embassies will close.

If anyone has more information on events please advise.