One of five sons born to an editor of the Post-Dispatch, Johns lost one of his legs at the age of seven when he was hit by a trolley car on Vernon Street. Being housebound, he spent many days composing poetry. He attended Central High School and the University of Missouri. He was editor of the humorous monthly, the "Missouri Oven."

After working as a deputy city marshall, Johns joined the staff of the Mirror. He became friends with Zoe Akins and Sara Teasdale, who also worked at the publication and helped him with his poetry. He reviewed plays, books, music and fine arts. Johns followed Akins and Teasdale to New York in 1911. Johns’ poem "Second Avenue" was one of more than nine thousand poems that was submitted for the New York publication, Lyric Year. His poem won the first place $500 prize. He moved back to St. Louis in 1917 and published his first book of poems, Asphalt and Other Poems. During this period he wrote poems that he would later publish in his 1926 poetry collection Wild Plum.

Johns worked at Gardner Advertising Agency during World War I and then moved back to New York to work for an advertising agency there. He was married twice and, in 1946, he took his own life.