Compared to the grand ceremony last time on Capitol Hill, this time around it was an intimate affair in the White House's Blue Room, conducted by Supreme Chief Justice John Roberts and witnessed by his family – wife Michelle and daughters Malia, 14, and 11-year-old Sasha.
And there was another key difference marking the ceremony out from 2009, when the chief justice recited the 35-word oath from memory, causing both he and Mr Obama to stumble over their words and have to repeat it a second time. On this occasion it was read out and executed perfectly – something which didn't escape the notice of president's younger daughter.
"Good job, Dad," Sasha told the commander-in-chief – who was sworn in shortly before noon on Sunday. He replied: "I did it," only to be told: "You didn't mess up." This drew laughter all round from the First Family.
Beginning his term as the 44th American president, Mr Obama put his left hand on the Robinson family bible – which has been Michelle's family since 1958, and swore to "faithfully execute the office" and to "preserve, protect and defend the Constitution."
Vice President Joe Biden was sworn in at a separate ceremony at his official residence by Supreme Court Justice Sonia Sotomayor, the court's first Hispanic justice.He had moved the event from noon to 8.15am so that Mrs Sotomayor could get a train to New York in time to promote her memoir My Beloved World.
The two small, private ceremonies were down to the calendar and the Constitution, which states that traditionally a president’s term begins at noon on January 20. This year, that date fell on a Sunday – the day of the week when inaugural ceremonies are not usual held.
So a second, more high profile public swearing-in is scheduled for Monday on the steps of the US Capitol, and a sizeable crowd of 800,000 people are expected to watch this from the National Mall. Beyonce will sing the national anthem and there'll be performances by Kelly Clarkson and James Taylor.
The Obama family started their inauguration celebrations on Sunday night, attending a concert at the Kennedy Center which featured Latino acts. On hosting duty was actress Eva Longoria, who has long been a supporter of Barack Obama.
The Desperate Housewife looked flawless in a strapless peach column dress at the event. Earlier in the day she attended a brunch in support of bipartisanship – encouraging opposing political parties, in this case Republicans and Democrats, to find common ground through compromise.
Joining Eva at the event was fellow actress Rosario Dawson, who said she was looking forward to enjoying the inaugural events with her mother Isabel, who is joining her in Washington DC. "I am excited about the next four years and possibly immigration reform," she said.