Chicago on Tuesday became the biggest US city to elect a black woman its mayor, as voters put their faith in an openly-gay political novice to tackle difficult problems of economic inequality and gun violence.

Lori Lightfoot, a 56-year-old former federal prosecutor and practicing lawyer who has never before held elected office, won the Midwestern city's mayoral race in a lopsided victory. She beat out Toni Preckwinkle, a career politician who is also black, by a wide margin of 74 to 26 percent with most ballots counted.