Jesus "Jesse" Sandoval beat incumbent Matthew Slowik on Tuesday for one of two available slots on the council.
Lydia Salazar Wibert handily retained her seat, picking up 13,211 votes, which was 2,000 more than any of the five other candidates.
Sandoval garnered 10,890 votes, and 9,733 voted for Slowik.
Mayor Acquanetta Warren said she hoped that Sandoval "would become part of the team."
She also said Slowik's loss was a surprise.
"It is something we did not expect," Warren said. "He is part of the team, and we expected him to win. It is a big surprise.
"Matt is a phenomenal person. He has dedicated his life to serving the public. He is a caring man who really cares about the future of kids .... He's involved with schools."
Warren has only talked briefly to Sandoval a few times and does not really know him.
Sandoval could not be reached for comment Wednesday.
Sandoval has said that he was running for the City Council "because we must form a partnership between the city, schools and the city businesses to keep Fontana moving in a positive direction."
Slowik and Wibert were seeking their first electoral wins after being appointed to the council two years ago, filling the seats of Janice Rutherford, who won a seat on the county Board of Supervisors, and Warren, who was
Sandoval has lived in Fontana for 45 years and is a 1977 graduate of Fontana High School. He works for the city of San Bernardino as a parks maintenance supervisor.
He has been a volunteer for the Fontana Police Department, a commissioner at the Fontana Parks and Recreation Department, a member of the Native Sons of the Golden West, and a coach for various youth softball and football teams.
Slowik is a lifetime resident of Fontana, has bachelor's and master's degrees in urban and regional planning and a master's in public administration. He is a senior land-use planner for San Bernardino County.
Slowik has served as chairman and vice chairman of the city's Planning Commission and Parks and Recreation Commission.
He could not be reached for comment Wednesday.