The 34-year-old was sacked from the role three years ago after falling out with coach Waqar Younis.
Fast-bowling legend Younis remains in charge, but Afridi, who led his country to the semi-finals of the Twenty20 in 2010, has insisted that both parties are ready to put the past behind them and introduce a no-fear approach to Pakistani cricket.
Afridi told reporters: "Whatever happened in the past is over and now I have started a new beginning.
"I will develop a fearless approach in the players and eradicate the fear of loss as a captain. This format is not for the chicken-hearted player."
Afridi replaces Mohammad Hafeez, who resigned in April following the team's exit from the World T20 in Bangladesh.