Illinois congressman Rahm Emanuel (L) was an adviser to President Clinton
Barack Obama has started forming his administration by asking Rahm Emanuel, a former adviser to President Clinton, to be his chief-of-staff.
US President-elect Obama is next expected to appoint a treasury secretary to tackle the country's economic crisis.
He has until his inauguration on 20 January to select his senior officials.
Mr Obama was elected the first black US president on Tuesday with a resounding win over Republican rival John McCain.
Mr Obama's transition team is to be run by John Podesta, a former chief-of-staff to President Bill Clinton; Pete Rouse, who was Mr Obama's Senate chief-of-staff; and close friend Valerie Jarrett.
No briefings or announcements are expected on Thursday, but Mr Obama's staff said that he would address the media by the end of the week.
Mr Emanuel is an Illinois congressman and tough Washington insider who has been strongly criticised by some Republicans for being too partisan, says the BBC's Jane O'Brien in Washington.
Although he has not formally accepted the job yet, if he does become chief-of-staff, he would be responsible for much of the internal management of the new administration.
But critics say his appointment could accentuate party divides, rather than heal them, as Mr Obama has pledged to do.
With the country in the throes of an economic slowdown and part of the global financial crisis, the post of treasury secretary will be a key post.
Likely contenders reportedly include former Treasury Secretary Larry Summers, and Timothy Geithner, the current head of the New York Federal Reserve.
Current Treasury Secretary Henry Paulson has pledged to work with Mr Obama to ensure a smooth transition, and is said to have already set up desks and telephone lines at the department where Mr Obama's incoming team can work between now and the inauguration.
There has been speculation Mr Obama will ask Defence Secretary Robert Gates to remain in his post.
Mr Gates is broadly respected by both parties and would reflect a more bipartisan administration, our correspondent says.
With the business of preparing for government under way, Mr Obama will from Thursday start receiving the president's daily CIA briefings, which will include updates on covert operations.
In another sign of the changing of the guard, Michelle Obama spoke by telephone with First Lady Laura Bush, who invited her to visit the White House.
Projected results from Tuesday's election have yet to be announced for the states of North Carolina and Missouri, which are believed to be too close to call.
Mr Podesta was a key figure in the Clinton administration
But with most precincts tallied, Mr Obama's share of the popular vote stands at 52.4%, compared with Mr McCain's 46.3%.
Turnout was reported to be extremely high - in some places "unprecedented" in what many Americans said they felt was a historic election.
The entire US House of Representatives and a third of US Senate seats were also contested in Tuesday's elections.
The Democrats increased their Senate majority by five seats to 56, including two independents, but fell short of the 60 needed to stop blocking tactics by Republicans. A further four seats are too close to call.
The Democrats also increased their majority in the House of Representatives, gaining 19 seats to give a total 254, leaving the Republicans with 173.