Obama hugged his wife and children Malia, 14, and Sasha, 11, before quipping: "I did it" to his youngest daughter.
The cheeky Sasha shot back: "You didn't mess up!"
Michelle Obama later sent a personal tweet saying: "Barack just took the official oath at the @WhiteHouse & used my grandma's bible for the ceremony. I'm so proud of him. -- mo."
The Constitution states that US presidential terms end at noon on January 20. When that date falls on a Sunday, there is a private swearing-in ceremony before public celebrations and a second oath taking the next day.
Four years on, Obama's status as the first black president in a nation born on a racial fault line almost seems like an afterthought now -- perhaps a sign of progress.
But poignantly, Obama will takes his second, second term oath of office on the federal holiday marking civil rights pioneer King's birthday.
In another historic echo, Obama will become the second president to be sworn in four times -- thanks to the Roberts stumble in 2009 and his double oath duty this year, joining Democratic icon Franklin Roosevelt.
Obama faces several boiling foreign crises likely to shape his legacy.
The US confrontation with Iran is fast-headed to a critical point with the specter of military action becoming ever more real the longer diplomacy over Tehran's nuclear program remains stuck in neutral.
And terror strikes that killed Americans in Benghazi and Algeria call into question Obama's election year sound bite that "Al-Qaeda is on the run," despite the killing of Osama bin Laden in Pakistan in 2011.