side, after being sworn in by the Supreme Court Justice Elena Kagan.
"So I will be reporting Monday morning at 9 o'clock," he told the awaiting media at the Capitol on Friday.
Besides his wife, he was joined by daughter Vanessa, brother Cameron, and his Senate staff, who presented him with a gift: the seat he say during his 28 years of service in the Senate.
Replacing Hillary Clinton as the top American diplomat, Kerry has an illustrious career spanning over three decades of public life.
For the last four years he was chairman of the powerful Senate Foreign Relations Committee.
A close confidant of Obama, Kerry, 69, in the last four years several times came to the rescue of Obama Administration whenever US relationship with Pakistan reached low ebb.
He has a personal relationship with top Pakistani leadership.
A Vietnam war veteran, Kerry played a key role in shaping the country's foreign policy and national security and on a range of issues including Afghanistan and Pakistan, nuclear nonproliferation, and global climate change.
As chairman of the Foreign Relations Committee, in 2010, Kerry was instrumental in renewing the New START Treaty, a vital nuclear arms reduction treaty with Russia that helps steer both countries away from dangerous nuclear confrontations.
In an interview to The Boston Globe, Kerry said the US President Barack Obama offered him the job of Secretary of State a week before United Nations Ambassador Susan Rice withdrew her name from contention, an earlier timeline than has been previously reported.
"He called me, actually a week before Susan got out of the thing," Kerry said.
"He called me and said, 'You're my choice. I want you to do this.' He asked me to keep it quiet. I did. I sat on it," he was quoted as saying.
The White House refused to comment on his interview.
In the interview, Kerry spelled out that Benghazi, embassy security, Iran and Syria would be some of his key priorities to begin with.
Kerry said he would be travelling, but would not try to break the record of his predecessor Hillary Clinton who travelled to a record 112 countries.