A former official in the Department of Homeland Security revealed on Wednesday that he was "Anonymous," the mysterious author of a newspaper column and book highly critical of President Donald Trump.

Miles Taylor, who served as chief of staff to former Homeland Security Secretary Kirstjen Nielsen, revealed his identity on Twitter and in a statement on Medium.com.

The identity of "Anonymous" had been a favourite guessing game in Washington since an opinion column appeared in The New York Times two years ago from a "senior official" who claimed he was a member of the "resistance" within the Trump administration.

In the column, Anonymous said, "many Trump appointees have vowed to do what we can to preserve our democratic institutions while thwarting Mr. Trump's more misguided impulses."

"Anonymous" followed up the Times column with a book called "A Warning" in November 2019 that chronicled dysfunction in the Trump administration.

In revealing his identity Taylor said he was a Republican and "wanted this President to succeed."

"But too often in times of crisis, I saw Donald Trump prove he is a man without character, and his personal defects have resulted in leadership failures so significant that they can be measured in lost American lives," Taylor said.

"I witnessed Trump's inability to do his job over the course of two-and-a-half years," he said. "Everyone saw it, though most were hesitant to speak up for fear of reprisals."

Since leaving the Trump administration, Taylor has been a contributor to CNN and has endorsed Democratic candidate Joe Biden for president.

"This is the least impressive, lamest political 'reveal' of all time," campaign press secretary Hogan Gidley said in an official statement, calling Taylor "just another standard-issue arrogant, Washington, DC swamp bro."

White House deputy press secretary Sarah Matthews responded to Taylor revealing his identity by calling him an "absolute loser."

"This is beyond embarrassing for (The New York Times) that they would grant anonymity to such a low-ranking official," Matthews said.