MacAnthony took over as chairman at Peterborough at the age of 30, making him the youngest chairman in the Football League. As a sign of his ambition, a printed note from MacAnthony was added to Peterborough United's match programme in August 2007. In it, he promised fans promotion from League Two to the Championship in two seasons, which was duly delivered, though the club were subsequently relegated to League One. MacAnthony became owner of the club in August 2007, buying the club for a nominal £1 after taking on the club's debts.