South Africa and Burundi also ignored appeals from UN Secretary-General Ban Ki-moon to reverse their decisions and have sent letters confirming that they are quitting the ICC.
Banjul's decision to pull out of the court struck a personal blow against the tribunal's chief prosecutor Fatou Bensouda, a Gambian lawyer and former justice minister.
Gambian Information Minister Sheriff Bojang charged that the ICC had been used "for the persecution of Africans and especially their leaders" while ignoring crimes committed by the West.
Gambia's withdrawal will take effect one year after the letter was received on November 4.
Kenya, Namibia and Uganda are among other African countries that have indicated they, too, are considering pulling out of the Rome statute, the ICC's founding treaty.