Do you participate in...,

[Silverobama]

This morning, there was a marathon even in our city. I was wondering if a friend of mine had joined the competition because he was crazy about that. I texted him and asked:

Do you participate in the marathon today and run through till the end?

Please help me with a natural sentence.

 

[emsr2d2]

This morning, there was a marathon [event] in our city. I was wondering if a friend of mine had joined the competition was running it because he was is crazy about that marathons/running. I texted him and asked:

Do you participate in Are you running the marathon today? and run through till the end?

Please help me with a natural sentence.

See above. You didn't need "event" in the first sentence. Just say "There was a marathon". Enough people know what that means to understand the sentence.
Your main sentence was far too long for the context. The last part was ungrammatical but I assume you were trying to ask him if he planned to actually finish the race (ie run all 26 miles). That's redundant. No one trains for and enters a marathon unless they plan to complete it.
You can take the phrase "run a marathon" as a set phrase.

Are you running the marathon next week?
Have you ever run a marathon?
My friend is running the marathon tomorrow.