Lyrics by Julia Ward Howe, written as she watched regiments of Yankee troops marching in to defend Washington, D.C. The tune is "John Brown's Body". Bolded phrases are titles from Bruce Catton's trilogy of American Civil War history books. Note the absence of The Coming Fury.

Mine eyes have seen the glory of the coming of the Lord
He is trampling out the vintage where the grapes of wrath are stored
He has loosed the fateful lightning of his terrible swift sword
His truth is marching on!

(chorus:)
Glory! Glory! Hallelujah! Glory! Glory! Hallelujah!
Glory! Glory! Hallelujah! His truth is marching on!

I have seen him in the watchfires of a hundred circling camps
They have builded him an altar in the evening dews and damps
I can read his righteous sentence by the dim and flaring lamps
His day is marching on!

(chorus)

I have read a fiery gospel writ in burnished rows of steel
"As ye deal with my condemners, so with you my grace shall deal."
Let the hero born of woman crush the serpent with his heel
Since God is marching on!

(chorus)

He has sounded forth the trumpet that shall never call retreat
He is sifting out the hearts of men before his judgement seat
O be swift, my soul, to answer him, be jubilant my feet!
Our God is marching on!

(chorus)

In the beauty of the lilies Christ was born across the sea
With a glory in his bosom that transfigures you and me
As he died to make men holy, let us die to make men free
While God is marching on!

(chorus)

He is coming like the glory of the morning on the wave
He is wisdom to the mighty, he is courage to the brave
So the world shall be his foot stool and the soul of wrong his slave
As God is marching on!

chorus
Amen! Amen!

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Thanks are in order to Byzantine, who corrected me on the second-to-last verse. Some later arrangements change it to "...let us live to make men free", a peace-time adaptation that wouldn't have rung true during the Civil War.

The troops were singing John Brown's Body as they marched. The Rev. James Freeman Clarke, who was watching them with the Howes, asked Ms. Howe if she could think up some more inspiring words for the rousing melody. That night at the Willard Hotel the opening line came to her in her sleep. She lit a candle, and completed the lyrics before dawn. She sold her poem to the Atlantic Monthly for ten dollars. It appeared on the front page of the February 1862 issue. Oliver Ditson and Company published the sheet music soon after.