Annie Armstrong (July 11, 1850 – December 20, 1938) was a lay Southern Baptist denominational leader instrumental in the founding of the Woman's Missionary Union.

Annie Walker Armstrong was born in Baltimore, Maryland[1] to tobacconist John Dunn Armstrong and his wife Mary Elizabeth Armstrong. She also had a brother named James. She came from a long line of prominent Baptists including her great-great-grandfather Henry Satre 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 African Americans, Native Americans, Chinese Americans immigrants, and indigent women.

In 1888, Armstrong led the creation of the Woman's Missionary Union, helping draft the constitution and serving as its first correspondent secretary (a position that functioned as executive director).
In her role as the head of the organization, Annie Armstrong facilitated communication between denominational leaders, local congregations and missionaries on the field. She was an extensive letter writer, handwriting 18,000 letters in one year alone.

During her tenure as head of the WMU, Armstrong refused a salary and traveled at her own expense on behalf of the WMU.
Caring for her own travel expenses until 1901, Miss Armstrong traveled great distances-3,300 miles in 21 days, visiting 19 places, and making 26 addresses. Besides writing leaflets for Woman's Missionary Union, Miss Armstrong, at the request of the editors, started a young people's Scripture department in Kind Words, a "Folks and Facts" column, and two departments in The Teacher. She was a frequent contributor to the two mission publications, Foreign Mission Journal and Our Home Field. In 1888, after conference with Henry Allen Tupper, secretary of the Foreign Mission Board, Miss Armstrong wrote by hand letters to all the societies, asking them to contribute to the first Christmas offering, which resulted in $2,833.49 for Lottie Moon in China. She led Woman's Missionary Union to enlarge its efforts in providing organizations for Negro Baptist women and children and in publishing literature for them.

As memorials to Miss Armstrong, Woman's Missionary Union voted in 1907 to give $5,000 to a Home Mission Board mountain school and $5,000 to a hospital in China. The Annie Walker Armstrong building, erected at Burnsville, N. C., was dedicated in 1908 in appreciation of her service. More permanent memorials are the Annie Armstrong Offering for Home Missions and the structure of Woman's Missionary Union, which she led in establishing.

Annie Armstrong died on December 20, 1938 in Baltimore, the year the WMU celebrated its fiftieth anniversary. She was buried in historic Green Mount Cemetery, with her parents and elder siblings. She has been inducted into the Maryland Women's Hall of Fame, and Southern Baptist Churches collect an Easter Offering for North American Missions in her name.