Porter's objective was to deal with a Confederate force near Hanover Court House, which threatened the avenue of approach for Union reinforcements that were marching south from Fredericksburg.

Firstly, the Pamunkey River, which ran roughly parallel to the Chickahominy, offered a line of communication that could enable McClellan to get around Johnston's left flank.

Secondly, McClellan anticipated the arrival of the I Corps under Maj. Gen. Irwin McDowell was scheduled to march south from Fredericksburg to reinforce his army, and thus, he needed to protect their avenue of approach.

[3] While skirmishing occurred all along the line between the armies, McClellan heard a rumor from a Virginia civilian that a Confederate force of 17,000 was moving to Hanover Court House, north of Mechanicsville.

They had departed from Gordonsville to guard the Virginia Central Railroad, taking up a position at Peake's Crossing, 4 miles (6.4 km) southwest of the courthouse, near Slash Church.

At about noon on May 27, his lead element, the 25th New York Infantry, encountered Col. James H. Lane's 28th North Carolina on a reconnaissance patrol at the farm owned by Dr. Thomas H. Kinney.

The New Yorkers, along with the 1st U.S. Sharpshooters, skirmished briskly with the Confederates until Porter's main body arrived, driving the outnumbered Rebels up the road in the direction of the courthouse.

General McClellan claimed that Hanover Court House was yet another "glorious victory over superior numbers" and judged it "one of the handsomest things of the war.

[9] A more significant impact than the actual casualties, according to historian Stephen W. Sears, was the effect on McClellan's preparedness for the next major battle, at Seven Pines and Fair Oaks four days later.

During the absence of Porter, McClellan was reluctant to move more of his troops south of the Chickahominy, which made his left flank a more attractive target for Johnston.