Definition of write someone in in English:
chiefly US (When voting) add the name of someone not on the original list of candidates and vote for them.
- The Chronicle and several other local papers exposed the plan after an 18-year old was recruited to run, but then changed his mind when he found out that he had been written in as a Democratic candidate.
- I shook his hand just before the primary up here and told him I was a registered Republican and I was writing him in on my ballot.
- Even though his name wasn't on the ballot, he was written in by nearly half of the voters.