Mr Ford took the oath in the oval office of the White House - which once held the secret microphones that caused Mr Nixon's downfall.
Mr Nixon was scheduled to be in the air, en route to his California estate at San Clemente, as Mr Ford took office at noon local time (4 a.m. New Zealand time).
Mr Nixon announced his decision to leave office - after two years of fighting off the tentacles of the Watergate scandal - in a calm and graceful speech televised across the nation and abroad.
Mr Nixon-the first United States President in history to resign - displayed neither malice nor vindictiveness towards the reporters, lawyers and congressmen who spearheaded the fight for his removal two and a-half years before the end of his second four-year term.
"Let me say I leave with no bitterness toward those who opposed me because all of us, in the final analysis have been concerned with the good of the country, however, our judgement may differ," he said.
REASON
Mr Nixon gave as the specific reason for his resignation the fact that he had lost, because of his involvement in Watergate, the basic support in Congress needed to pass his legislative programmes.
By contrast, Mr Ford said last night: "I don't think I have a single enemy in Congress. I think tomorrow I can start out working with Democrats and with Republicans in the House, as well as in the Senate, on the problems, serious ones, which we have at home."
Mr Ford is expected to pursue most of Mr Nixon's policies, but gone with the outgoing President may be his Administration's "gut hostility" towards such issues as amnesty for Vietnam draft dodgers and recognition of the Fidel Castro Government in Cuba.
His style in the White House will certainly be a far cry from Mr Nixon's - open and co-operative where Mr Nixon and his aides tended to be secretive and suspicious of outsiders.
TWO QUESTIONS
But two large question marks hang over Washington - who will be Vice-President and will Mr Nixon have to face criminal charges?
In his brief press conference yesterday, Mr Ford gave no indication of any answer to the first question although he did announce that Dr Henry Kissenger had agreed to stay on as Secretary of State.
However, one news agency reported last night it was thought the country was ready for a negro as Vice-President and suggested Massachusetts Republican Senator Edward Brooke, the only black in the United States Senate, had been suggested.
Other Vice-Presidential candidates include Mr Elliott Richardson, who was Attorney-general under Mr Nixon, and Mr Melvin Laird, a former Defence Secretary who if not nominated for the top post, is regarded as certain to be included in Mr Ford's Administration in some capacity, possibly as White House chief of staff.
NO AGREEMENT
The Watergate prosecutor, Leon Jawoski, who presumably would have a say in whether criminal charges are brought against Mr Nixon, said yesterday he had "no agreement or understanding of any sort" that led to Mr Nixon's resignation.
There are efforts under way in Congress, however, to enact a resolution urging that no criminal prosecution be undertaken against Mr Nixon.
As a private citizen, Mr Nixon will immediately become liable to indictment should a grand jury decide to charge him. The Watergate grand jury already has named him an unindicted co-conspirator in the cover-up for, which six of his former aides are due to go on trail on September 9.
Federal law, however, does not bar co-conspirators from being indicted later in the same case.
A spokesman for Mr Jawoski said the prosecutor was informed of Mr Nixon's decision by "someone in the White House," though he declined to say whom. He also declined to elaborate on Mr Jaworski's statement or to indicate whether any criminal action against Mr Nixon is contemplated.