With the senator and wife Theresa Heinz-Kerry standing beside him, the president said Kerry's "entire life has prepared him for this role."
"As the son of a foreign service officer, he has a deep respect for the men and women of the State Department; the role they play in advancing our interests and values; the risks that they undertake and the sacrifices that they make along with their families," he said.
Obama said the senator's service as a Vietnam veteran taught him the "responsibility to use American power wisely, especially our military power," and the personal responsibility of sending troops into harm's way.
Kerry, 69, the Massachusetts Democrat who was his party's nominee for president in 2004, chairs the Senate Foreign Relations Committee, which makes him a logical pick for the post. And he is unlikely to face fierce opposition from senators across the aisle.
The president credited Kerry with having played a "central role" in foreign policy debates for the past three decades, including ratification of the START nuclear treaty with Russia.
"I'd say that one of the more exceptional things we've seen in recent decades was when John helped lead the way, along with folks like [Sen.] John McCain and others, to restore our diplomatic ties with Vietnam," he continued. "And when he returned to the country where he and so many others had fought so long ago, it sent a powerful message of progress and of healing."
It was during Kerry's presidential campaign in 2004 that Obama gave the keynote address at the Democratic National Convention widely attributed to helping launch his Senate and presidential career. The president thanked him for that opportunity, and the career path that followed.
"I was proud to serve with him on the Foreign Relations Committee, under the tutelage of Joe Biden, and where we all became friends," Obama said.
Kerry also served as Mitt Romney's stand-in during the 2012 campaign's debate preparations. It was an experience that solidified their friendship, Obama concluded.
Secretary Clinton was not present for the announcement, as she recovers from a concussion she sustained from fainting. The president acknowledged the secretary and his national security team for transitioning the country through two wars and an expanded presence in a surging Asia.
"Over the last four years, Hillary's been everywhere -- both in terms of her travels, which have seen her represent America in more countries than any previous secretary of state, and through her tireless work to restore our global leadership," he said.
In a written statement, Clinton said her relationship with the Massachusetts lawmaker began decades ago."John Kerry has been tested -- in war, in government, and in diplomacy. Time and again, he has proven his mettle," it reads. "I remember watching young Lieutenant Kerry's testimony before the Senate Foreign Relations Committee many years ago and thinking that I had just seen a man of uncommon courage and conscience."
Kerry's nomination is the only one expected from the White House this afternoon, although other cabinet members, including Secretary of Defense Leon Panetta, are expected to leave the administration in the coming weeks.
An earlier possible State Department nominee, U.S. Ambassador to the United Nations Susan Rice, withdrew from consideration for the position when Republicans began to mobilize against her. At issue was Rice's involvement in the Obama administration's response to the deadly Sept. 11 attack on the U.S. consulate in Benghazi, Libya.
Kerry's nomination will place a respected statesman and party elder in a high-profile cabinet position. But it will also create an opening in the Senate.
Sen. Scott Brown, the moderate Republican who lost his bid for re-election in November to consumer advocate Elizabeth Warren, is expected to consider a run for Kerry's seat.