Gates, 67, departed as Pentagon chief in June after four and a half years serving under former President George W. Bush and then Barack Obama. He took over the position from Donald Rumsfeld who resigned amid criticism over his handling of the Iraq war.

The memoir will look at the key events during Gates' tenure, including US strategy in Afghanistan, the withdrawal of troops in Iraq and the Obama administration's repeal of the "Don't Ask, Don't Tell" laws that prevented gay and lesbians in the military from serving openly, publisher Alfred A. Knopf said.

"I want to tell my story of constant conflict abroad and in Washington. I will share insights gleaned from my experience of working for two very different presidents in two administrations of very different political stripes," Gates said.