Trump fired Corey just a month before he is to secure the official nomination at the party's convention in Cleveland. The sacking highlighted a broader adjustment by the campaign as it grapples with a late start to fund-raising, anxiety among party leaders and a weakened staff.
Trump had faced questions from allies and donors over whether Lewandowski has got the potential to direct a battle against Trump's main rival Hillary Clinton. Among those who had voiced concern was Reince Priebus, the chairman of the Republican National Committee, who informed Trump last week that relations between his committee and Mr. Lewandowski had become increasingly strained.
Republicans have welcomed the decision as a positive step, but they said that Trump need to follow this by consistent changes in performance.
Lewandowski was shown the door at a Monday morning meeting with Trump and his two older sons, Eric and Donald Jr., said two others briefed on the meeting. Trump and Lewandowski had what was described as a "very open conversation."
Lewandowski spent most of his time on the campaign trail with the candidate, and he had handed over day-to-day aspects of the operation to the chief strategist, Paul Manafort. Lewandowski sometimes made headlines about himself that overshadowed his boss. He was also once charged with misdemeanor battery but the charge was later dropped.
Trump did not announce whether he would appoint someone new as his campaign manager. It is learned that the existing Trump team believed most of the duties had already been assumed by other people, principally Manafort.