After five days of political drama following the general election, the Conservative leader was finally announced as the British premier after his party agreed to form a coalition government with the Liberal Democrats.
Pictured with his proud and expectant spouse Samantha by his side, the 43-year-old – who has become the youngest prime minister since 1812 – delivered his first speech in the role outside the couple's new home at Number 10 on Tuesday evening.
His address came after a meeting with the Queen at Buckingham Palace, during which he officially accepted the monarch's offer to form the next government.
And as the former Etonian and his family begin to adjust to his new political position, his predecessor Gordon Brown is preparing to embark on life away from Downing Street.
The Labour leader bid an emotional farewell as he and his wife left their former home for the last time, the dad-of-two's voice cracking with emotion as he formally resigned the premiership.
Joined by supportive Sarah, Mr Brown said goodbye to "the second most important job I could ever hold" after being a husband and father.
In the short speech outside the residence, he said it had been a privilege to lead the country.
He also paid tribute to his wife's "unwavering support and her love" and to his sons, six-year-old John and Fraser, three, "for the love they bring to our lives."
Then, hand in hand, the Brown family left Downing Street for the very last time.
The former prime minister was taken immediately to Buckingham Palace to formally resign his office to the Queen, before flying to Scotland with Sarah and the boys to their North Queensferry home.