"The Giants' 3-1 lead in the World Series has electrified the city and brought us all together," Mayor Gavin Newsom said in a statement.
The team needs one more win against the Texas Rangers to win the series.
Newsom's office is collaborating with the Recreation and Park Department, which organized a similar public showing for a number of World Cup games this summer.
Alcohol will not be sold or permitted at the family-friendly event tonight. Attendees are encouraged to arrive early and secure their spots to watch the game.
In celebration of the team's post-season success, a number of San Francisco buildings have been lit up orange, including City Hall, the War Memorial Opera House and Coit Tower.
The buildings will continue to glow orange until the end of the World Series, the mayor said.
Game 5 will be played in Arlington, Texas, with the first pitch thrown just before 5 p.m. Pacific Standard Time.