early 13c., "doughty fighting man, valorous combatant," also (c. 1300) "one who fights on behalf of another or others, one who undertakes to defend a cause," from Old French champion "combatant, champion in single combat" (12c.), from Late Latin campionem (nominative campio) "gladiator, fighter, combatant in the field," from Latin campus "field (of combat);" see campus.
The word had been borrowed earlier by Old English as cempa. Sports sense in reference to "first-place performer, one who has demonstrated superiority to all others in some matter decided by public contest or competition" is recorded from 1730.
"to fight for, defend, protect, maintain or support by contest," 1820 (Scott) in a literal sense, from champion (n.). Figurative use, "maintain the cause of, advocate for" is by 1830. Earlier it meant "to challenge" (c. 1600). Related: Championed; championing.