"There was no deal to be done," a senior Labour source told the BBC, making Brown's resignation the next logical step.
In his first speech as prime minister, Cameron acknowledged the role Brown had played in politics over the past few years. "On behalf of the whole country I'd like to pay tribute to the outgoing prime minister for his long record of dedicated public service," Cameron said.
Moments earlier Brown had treated his successor with similar respect. "I wish the next prime minister well as he makes the important choices for the future," Brown said before heading out of the official Downing Street residence to appear before the Queen in order to tender his resignation, his two children and wife by his side.
In the traditionally fast handover of power, just hours after the Browns left the Camerons entered Downing Street as their new home.
Obama wished his former colleague farewell, and thanked him for his friendship. "He provided strong leadership during challenging times, and I have been grateful for his partnership," the president said in a statement.
ABC News' Jean-Nicholas Fievet contributed to this report.