Annie Armstrong was born in Baltimore, Maryland to tobacconist John Dunn Armstrong and his wife Mary Elizabeth (Walker) Armstrong. She also had a brother named James. She came from a long line of prominent Baptists including her great-great-grandfather Henry Sater who help establish the first Baptist church in Maryland.
At the age of 20, she accepted Christ as her Savior under the preaching of Dr. Richard Fuller at Seventh Baptist Church (now Seventh Metro Church). It was there that she had a "born again" experience and was equipped to be a missionary. Later, she was among 100 Seventh Baptist Church members who established Eutaw Place Church (now Woodbrook Baptist Church). The church was pastored by Richard Fuller, the third president of the Southern Baptist Convention, who was heavily involved in missionary activities.
She worked with various Baltimore missionary organizations ministering to orphans, African Americans, Native Americans, Chinese Americans immigrants, and indigent women and families.