McAlpin attended public school for a time, then graduated from Phillips Academy in Andover, Massachusetts, in 1861.

In 1874 McAlpin attained the rank of first lieutenant in the 71st Infantry Regiment (New York) where he was promoted in 1885 to colonel, a role he retained until his military retirement in 1887.

He aggressively cut dead wood from the ranks and reorganized the officer ranks to the extent that the "Army and Navy Journal" called it on July 18, 1885 "virtually a new regiment, so much has its personnel changed during the past six months..."[2] The Journal placed the credit squarely on McAlpin's shoulders writing, "Colonel Edwin A. McAlpin, the but recently elected commander, has certainly developed energy, pluck and good sense in the management of his organization, which has, in turn, been followed by most encouraging results..."[3] After retiring from the service he was appointed Adjutant General of the State by Governor Levi P. Morton, in 1895 with the rank of Major General.

As befitted a prominent person at that time, the couple chartered a train to bring guests from New York City and return them at the end of the evening.

[5] Consisting of 27 rooms on a landscaped plot of 6 acres (24,000 m2), the house had 10 baths, large stables, a garage, some greenhouses, and a commanding view of the Hudson River.

He held several local offices in his home at Ossining, including: General McAlpin owned several large tracts of real estate in Manhattan, inherited from his father.