Yes, it works in the opposite direction. However, do not exceed its original ratings, both voltage and current. Suppose you have a transformer rated for 120 V in and 12 V out, a 10:1 turns ratio.

Are transformers bidirectional?

Transformer can handle power flow in both the directions, forward and reverse. This actually happens in case of interconnecting transformers. Either of the two windings can become primary (drawing power from source) and the other winding becomes secondary, delivering power to load. So it is bidirectional.

Can transformers be used backwards?

Yes, you can use the transformer in reverse, but note that the ratio is usually adjusted up by 5-10% to allow for the voltage loss under rated load due to winding resistance. When you use it in reverse, that will result in a lower output voltage than expected.