The company announced in June that it planned to remove the 140-character limit from its direct messaging feature.
DM allows users to have private conversations about the memes, news, movements, and events that unfold on the micro-blogging platform.
"The aim is to make the private side of Twitter just as fulfilling as the public side," the company said.
Earlier this year, the company had launched Group Direct Messages, where multiple users could chat at once and any user could message another privately, irrespective of the fact that they might not be following each other.
The update will be available to all users worldwide, who log into Twitter.com, TweetDeck and Twitter-owned-and-operated applications.
The company said it will support reading and writing long DMs for Android, Twitter for Mac and TweetDeck.
Mobile web users will be able to receive long DMs, but not send them.
"SMS DMs are still limited. If a user sends an SMS DM longer than 140 characters, Twitter will split it into multiple messages. While the first message will be sent as a DM in such a case, the remaining characters will post as Tweets," it said.