The ads will show up even if the promotion is from a company that a person hasn't chosen to follow. Until now, Twitter had only displayed ads that users were tracking.
As has been the case since Twitter began showing ads last year, the promotions must comply with the online messaging service's 140-character limit.
The ad expansion marks a major step in Twitter's attempt to make more money from its more than 100 million actively users. Twitter says the audience is now sending about 230 million tweets a day.
Twitter CEO Dick Costolo told reporters that the five-year-old company still hasn't set a timetable to go public.
