Heavy rains had turned the roads to quagmires by June 1 and Sherman had been forced to return to the railroad to supply his men.

Johnston's new line (called the Brushy Mountain Line) had been established by June 4 northwest of Marietta, along Lost Mountain, Pine Mountain, and Brush Mountain.

On June 14, following eleven days of steady rain, Sherman is ready to move again.

While on a personal reconnaissance, he spots a group of Confederate officers on Pine Mountain and orders one of his artillery batteries to open fire.

Lieutenant General Leonidas Polk, the "Fighting Bishop," is killed and Johnston withdraws his men from Pine Mountain, establishing a new line in an arc-shaped defensive position from Kennesaw Mountain to Little Kennesaw Mountain.

Johnston's Army of Tennessee has settled into the Kennesaw line, consisting principally of the twin elevations of Big Kennesaw Mountain and Little Kennesaw Mountain, and the pursuing Federal forces under Sherman had begun to probe this new line in search of weak spots on June 19

After judging the Kennesaw line to be too strong to take by regular assault—even though he will attempt to do just that five days later—Sherman decides to fix Johnston's line in place with his left wing, the Army of the Tennessee, under McPherson, while maneuvering his center and left wing, the Army of the Cumberland, under Thomas, into position to turn Johnston's left flank somewhere south of the Powder Springs Road.

In obedience to Sherman's orders, Thomas moves the XX Corps, under Major General Joseph Hooker, into the area; Hooker will be supported in this operation by the single-corps Army of the Ohio, under Schofield, who will guard Hooker's far right.

Johnston correctly anticipates Sherman's movements, and decides to counter them by moving one of his three corps, under Hood, from its reserve position near Marietta south and west along Powder Springs Road to the vicinity of Mount Zion Church; this will both extend his left and counter Sherman's turning movement.

Hood, ordered to pull out of line on June 20, had begun the movement on the morning of June 21.

His corps passes through Marietta and is in place by June 22.

Hood's corps attempts an unsuccessful attack at Peter Kolb's farm (the Battle of Kolb's Farm) south of Little Kennesaw Mountain.

Major Genera William W. Loring succeeds to command Polk's corps.

The battle has demonstrated Hood's main deficiency as a battlefield commander: his willingness to attack without adequate reconnaissance.

He will go on to make the same error, this time as an army commander, at three future engagements in the Atlanta Campaign—the Battle of Peachtree Creek, the Battle of Atlanta, and the Battle of Ezra Church—with exceedingly costly results.

On the Federal side, the victory is marred by growing friction between Sherman and Hooker.

Sherman, stalled fifteen miles (twenty-four kilometers) north of Atlanta, is in a difficult position.

He cannot continue his strategy of moving around Johnston's flank because of the impassable roads, and his railroad supply line is dominated by Johnston's position on the top of six hundred and ninety-one feet (two hundred and eleven) Kennesaw Mountain.

He reports to Washington "The whole country is one vast fort, and Johnston must have at least fifty miles (eighty kilometers) of connected trenches with abatis and finished batteries.
We gain ground daily, fighting all the time.... Our lines are now in close contact and the fighting incessant, with a good deal of artillery. As fast as we gain one position the enemy has another all ready.... Kennesaw ... is the key to the whole country."

Deciding to break the stalemate by attacking Johnston's position on Kennesaw Mountain, Sherman issues orders on June 24 for an 8 a.m. attack on June 27.

Sherman's armies suffer about three thousand casualties in comparison to Johnston's one thousand.

The Union general, not initially deterred by these losses, had twice asked Thomas to renew the assault.

"Our loss is small, compared to some of those [battles in the] East."

The Rock of Chickamauga replies, however, "One or two more such assaults would use up this army."

A few days later Sherman will mournfully write to his wife, "I begin to regard the death and mangling of couple thousand men as a small affair, a kind of morning dash." (McMurry, Richard M. Atlanta 1864: Last Chance for the Confederacy. Lincoln: University of Nebraska Press, 2000. p 111).

Kennesaw Mountain is not Sherman's first large-scale frontal assault of the war, but it is his last.

He had interrupted his string of successful flanking maneuvers in the Atlanta campaign for logistical reasons, but also so that he could keep Johnston guessing about the tactics he would employ in the future.

In his report of the battle, Sherman writes, "I perceived that the enemy and our officers had settled down into a conviction that I would not assault fortified lines. All looked to me to outflank. An army to be efficient, must not settle down to a single mode of offence, but must be prepared to execute any plan which promises success. I wanted, therefore, for the moral effect, to make a successful assault against the enemy behind his breastworks, and resolved to attempt it at that point where success would give the largest fruits of victory." (Liddell Hart, B. H. Sherman: Soldier, Realist, American. New York: Da Capo Press, 1993. p. 266. First published in 1929 by Dodd, Mead & Co.)

Kennesaw Mountain is usually considered a significant Union tactical defeat.

The opposing forces have spent five days facing each other at close range, but on July 2, with good summer weather at hand, Sherman sends the Army of the Tennessee and Stoneman's cavalry around the Confederate left flank and Johnston is forced to withdraw from Kennesaw Mountain to prepared positions at Smyrna.