“Say more about what’s happening! Rolling out now,” said an official tweet from the social network, which is seeking to broaden its appeal.
The new policy exempts media attachments such as photos, videos and polls from the character limit, as well as tweets that are quoted in a retweet.
The move comes as Twitter’s efforts to increase its user base and engagement have been sputtering, raising questions about its growth trend.
Amid reports that Twitter may be seeking ways to cut costs or even sell itself, the San Francisco-based service has been adding new features including live video.
The latest move eases but does not entirely eliminate the 140-character limit, which was set due to mobile phone text messaging constraints in place when Twitter launched in 2006.
Analysts have said Twitter needs to find new ways to boost its appeal beyond a core of celebrities, politicians and journalists, with its user base stagnant for the past year.
In its last quarterly update, Twitter said the number of monthly active users edged up to 313 million, up three percent from a year ago and only slightly more than the 310 million in the prior quarter.
Twitter has yet to post a profit, even as it has ramped up its efforts in advertising.