Walsh attended The English High School in Boston and graduated in 1886.

From 1896 to 1897, Walsh worked as a solo practitioner, and in 1898 went into partnership with Charles Donagh Maginnis and Matthew Sullivan named Maginnis, Walsh and Sullivan.

[1][3] Journalist Lucien Price wrote that Walsh "was a remarkable designer, a water colorist of distinction, one of several famous architects trained in the office of Peabody and Stearns, and a lover no less of life than of his art.

[5] Walsh became a member of the American Institute of Architects in 1901 and was elected a fellow in 1925.

In 1899, Walsh married Marian Adams Wright and together had three daughters and a son.