Mr Dowd, who was the lead lawyer for the federal special counsel probe of Russian meddling in the 2016 presidential election, reportedly stepped down after concluding Donald Trump was increasingly ignoring his advice.
Other reports suggest the President was becoming increasingly unsure of Dowd’s ability to handle special counsel Robert Mueller.
In an email to The Washington Post, Dowd wrote: “I love the President and wish him well.”
Mr Dowd had been in the role since last summer, taking over when Trump’s longtime personal lawyer Marc Kasowitz stepped down.
The move comes days after Trump beefed up his legal team with a lawyer who accuses the FBI and US Justice Department of trying to frame Trump with false charges of colluding with Russia during the 2016 election campaign, possibly signalling a more aggressive drive to discredit Special Counsel Robert Mueller.
Washington lawyer Joseph diGenova will join the legal team this week, according to attorney Jay Sekulow, who also represents Trump.
Last week, a person familiar with the matter told Reuters that veteran Washington lawyer Emmet Flood is under consideration for a White House job assisting Trump with the Russia probe.
Mueller is investigating possible collusion between the Trump campaign and Russia to influence the 2016 election, and President Trump has recently started criticising Mr Mueller by name as the investigation develops.
Moscow denies any interference and Trump has said there was no collusion.
More to follow…