He was left an orphan at the age of eleven, the eldest of six siblings; he dropped out of school and became a "cash boy" at Chapman's department store.

Cary was elected a member of the board of aldermen of Milwaukee in 1900 and was reelected in 1902 for the term ending in 1904.

Cary was elected as a Republican to the Sixtieth Congress, representing Wisconsin's 4th congressional district.

In 1912, he initially sought renomination as a Republican, but switched and announced he would run for the Democratic nomination as a "non-partisan" candidate.

He was an unsuccessful candidate for renomination in 1918 to the Sixty-sixth Congress, losing the Republican nomination to John C. Kleczka.