While he may have been elected by US voters back in November, the process of formally naming president-elect Barack Obama to the post only began Monday, dpa reported.
State representatives from around the country gathered to cast their ballots under the country's complex Electoral College system, officially making Obama the first African-American to capture the White House.
Some 538 electoral votes are divided among the 50 US states according to their population size. Each presidential candidate is awarded a portion of those votes based on the results of the November 4 election.
Obama won 53 per cent of the popular vote compared to 46 per cent for his Republican rival John McCain. But more importantly he won 365 electoral votes, to 173 for McCain. In all but two states, the winner of the popular vote wins all that state's electors.
The 538 so-called electors - made up primarily of activists named by each political party - gathered separately in state capitals to formally cast their ballots. There is little suspense involved, though technically the electors can vote whichever way they wish.
"This is a great day in America," said Pennsylvania's Electoral College President William George after the state's electors cast their 21 votes for Obama.
The US Congress will still have to count and approve the electoral vote in a joint session of both the Senate and House of Representatives on January 8.
Obama will take office 12 days later, January 20, in an inauguration ceremony that is expected to attract millions of onlookers to Washington.
Obama plans to travel by railroad to the Washington swearing-in ceremony, starting in Philadelphia and making stops in running mate Joe Biden's home town of Wilmington, Delaware; and Baltimore, Maryland; his transition team announced Monday.