early 15c., trophe, "an overwhelming victory;" 1510s, "a spoil or prize of war," from Old French trophée (15c.) from Latin trophaeum "a sign of victory, monument," originally tropaeum, from Greek tropaion "monument of an enemy's defeat," noun use of neuter of adjective tropaios "of defeat, causing a rout," from trope "a rout," originally "a turning" (of the enemy); from PIE root *trep- "to turn."
In ancient Greece, spoils or arms taken in battle and set up on the field and dedicated to a god. Figurative extension to any token or memorial of victory is first recorded 1560s. As "a symbolic representation of a classical trophy" from 1630s.
Trophy wife "a second, attractive and generally younger, wife of a successful man who acquires her as a status symbol" was a trending phrase in media from 1988 ("Fortune" magazine did a cover story on it in 1989), but is older in isolated instances.
Variations on this theme ['convenience-wife'] include the HOSTESS-WIFE of a businessman who entertains extensively and seeks a higher-level, home-branch version of his secretary; the TROPHY-WIFE — the woman who was hard to get because of birth or wealth or beauty — to be kept on exhibition like a mammoth tusk or prime Picasso ... [Phyllis I. Rosenteur, excerpt from "The Single Women," published in Philadelphia Daily News, Dec. 12, 1961]
The excerpt distinguishes the trophy wife from the "showcase wife," "chosen for her pulchritude and constantly displayed in public places, dripping mink and dangling diamonds," which seems more to suit the later use of trophy wife.