Mixing vitriol with snippets of gossip that could only come from within the White House, his tweets enraged officials who finally identified him last week after a long-running internal probe, the Daily Beast reported.
His targets ranged from his fellow White House aides who he described as "sh----" to Mr Kerry, who he joked was "boring the bejesus out of everyone" during meetings.
"I feel sorry for John Kerry's press handlers, who are cleaning up one s--- storm after the other he is creating on his current Asia swing," Mr Joseph tweeted during the secretary of state's visit to Asia in April.
He added that Republicans were "on to something" when they accused Mrs Clinton of a "whitewash of accountability" following the attack on the US consulate on Benghazi.
In more vicious tweets he called Liz Cheney, daughter of Dick Cheney, a "fat pig" and speculated about the sexuality of Lindsey Graham, an unmarried Republican senator.
On his account he described how he "unapologetically says what everyone else only thinks".
A man who resembled Mr Joseph refused to come to the door of his home in Alexandria, Virginia, on Wednesday but Mr Joseph released a written apology to Politico.
“What started out as an intended parody account of DC culture developed over time into a series of inappropriate and mean-spirited comments," he said. "I bear complete responsibility for this affair and I sincerely apologise to everyone I insulted.”
Aides in the White House and Senate expressed their shock that Mr Joseph, who had progressed rapidly through Washington's hierarchy, was behind the account.
"It's wild," said one Senate staffer. "He knew a lot and was well informed, certainly a tad full of it, strutting around that he worked at the White House."
Mr Joseph was a director on the White House's nuclear non-proliferation team and was involved in delicate discussions on Barack Obama's policy towards Iran.
A graduate of the prestigious Georgetown and Princeton universities he worked at both the State Department and the Senate before moving to the White House in August 2011, shortly after he set up the Twitter account.
