Several members of the Board of Supervisors, police Chief George Gascon, SFMTA Executive Director Nathaniel Ford and other city officials and department heads joined Newsom at the signing ceremony.
The budget agreement, reached after weeks of lengthy negotiations with the Board of Supervisors, closed a $482.7 million deficit.
Newsom praised public employee unions for making significant concessions -- more than $240 million in wage and other concessions have been made or are pending approval by the unions, he said.
"Once again, San Francisco has shown that by working together, we can balance our budget without new taxes, while still making vital investments in job creation, public safety, education and vital public health and family services," Newsom said.
The budget included steep cuts to most city departments, as well as reductions in overtime.
Additionally, more than 300 city workers will be laid off, though police and firefighters were protected.
Board of Supervisors President David Chiu noted after today's ceremony that the approved budget included about $140 million in "uncertain revenues" from the federal and state governments.
Chiu said that in the next six months, San Francisco will learn whether it will receive all of that money or only a portion, in which case additional cuts are expected.
That comes amid further uncertainty about next year's budget cuts, for which city department heads are already preparing, Chiu acknowledged.
Newsom's budget, submitted June 1, prioritized funding for construction projects and street repaving, jobs, public safety and fighting homelessness. He said the budget also protected public health and social services for the most vulnerable.
The Board of Supervisors then negotiated about $44 million in restorations for additional health and social services, and agreed to fund Newsom initiatives on homelessness and education.
Other budget reforms included reducing management salaries and eliminating 613 positions.
Newsom said the city now has the lowest number of employees since