However, the 140-character limit on tweets will remain in place.
"We've done a lot to improve Direct Messages over the past year and have much more exciting work on the horizon. One change coming in July that we want to make you aware of now (and first!) is the removal of the 140 character limit in Direct Messages," Twitter Product Manager (Direct Messages) Sachin Agarwal said in a blogpost for developers.
"You may be wondering what this means for the public side of Twitter. Nothing! Tweets will continue to be the 140 characters they are today," he added.
In April this year, Twitter had started giving users the option of receiving private direct messages from people they do not "follow" on the website.
Earlier only individuals that followed each other on twitter were able to exchange direct messages.
The company has grown its monthly active users by 18 per cent over last year to 302 million.