He has authored several poetry collections Far-Fetched (2015), Sources (2008), a finalist for the National Book Critics Circle Award for Poetry, Aversions (2004), Mosses and Lichens (2019) and Telepathy (2001).

His literary criticism and prose writing includes Precipitations: Contemporary American Poetry as Occult Practice (2002) and Creaturely and Other Essays (2009).

He was considered a lyrical poet having stated being influenced by W. B. Yeats.

According to the Poetry Foundation, "Johnston whittles the lines of his poems, compressing imagery that is at once allusive and immediate."

Johnston was awarded the Friends of Literature prize by the Poetry Foundation for his poems New Song and A Close Shave.