We use “congratulations on” when you are discussing an event and “congratulations for” when you are discussing the reason for the congratulations.

I want to send you congratulations on your wedding day.

I’d like to send the team congratulations for their outstanding work. 

“Congratulations on” is by far the most common way to congratulate someone on something.

We wish to send you congratulations on the birth of your son.

The preposition “on” helps the noun “congratulations” connect to the object(the event or achievement).

We use ”for” with “congratulations” when we want to make it clear what we are congratulating the person for(the reason).

This is a slightly nuanced difference in meaning and is a common use of the preposition “for”. 

Congratulations for being the first person to reach the South Pole.

It is important to understand that you can often also use “congratulations on” in this situation.

Congratulations on being the first person to reach the South Pole.

The difference is that when we use”for” we are stating the reason why we are giving the congratulations and “on” as the preposition when we just want to congratulate someone generally.

We use “congratulations to” when we want to direct our congratulations in the direction of a person.

Huge congratulations to the bride and groom.

I want to send congratulations to you for your recent promotion.

We usually use “congratulations on”  when congratulation someone on the birth of a child..

Congratulations on the arrival of your new baby.

We usually use “congratulations on”  when congratulation someone on getting married..

Congratulations on getting married.

We usually use “congratulations for”  when congratulation someone on getting a new job..

Congratulations for getting a new job.

We can also use “congratulations on”.

Congratulations on getting a new job.

We usually use “congratulations on”  when congratulation someone on graduating high school or college.

Congratulations on finishing high school.

We usually use “congratulations on”  when congratulation someone for an achievement..

Congratulations on your achievement of best tennis player this year. .