"Among all the keywords, hashtags, and phrases that proliferated throughout the year, one topic surfaced repeatedly," Twitter said in a blog post yesterday.
"Twitter users found the Iranian elections the most engaging topic of the year."
The San Francisco-based service that lets people broadcast news in short text messages using computers or mobile telephones was a primary communications tool by protesters in Iran angered by the results of their presidential election.
Dead singer Michael Jackson was the most tweeted about person, while Harry Potter was the film that caused the most Twitter buzz, according to the internet firm.
Google Wave - which allows email or instant messages to blossom into shared online arenas where anyone in the exchange can edit documents, add digital content, or comment at any time - was the most tweeted about technology, according to Twitter.