The council voted 13-0, with Councilman Kevin de León casting a vote even though he was not in the chamber.
Bass signed the declaration as a method to unlock tools and powers to "make sure we are using every resource possible" to address homelessness, claiming that it marked a "sea change" and "monumental shift" in the city's approach.
"Using the emergency order is our ability to fast-track things," Bass said.
She added: "My mandate is to move Los Angeles in a new direction with an urgent and strategic approach to solving one of our city's toughest challenges and creating a brighter future for every Angeleno."
The declaration -- which is scheduled to last six months -- allows Bass to take more aggressive executive actions to confront the crisis, though the City Council will have to sign off on it every 30 days.
"The setting of a specific time frame allows for actions to be taken to make permanent, necessary structural changes," the declaration reads.
Whether to continue the state of emergency will be evaluated by several indicators of progress, including the number of encampments and housing placements, and how much more flexibility city departments are allowed through the declaration.
City Council President Paul Krekorian signaled that he will work with Bass, saying in remarks at the mayor's inauguration on Sunday that Bass will have a "very strong partner in the Los Angeles City Council."
"The city is known throughout the world for its emergency response," Krekorian said. "Starting today, under Mayor Bass, we are going to bring that same vigor, that same sense of urgency, that same gathering of resources to respond to this emergency as well -- the humanitarian emergency that 40,000 people are suffering from tonight."
The last time a mayor declared a local emergency related to homelessness was in 1987, when Mayor Tom Bradley cited the effect of winter weather on people experiencing homelessness, according to the declaration. The conditions now, the declaration claimed, are "even more dire."
There are an estimated 41,980 unhoused people in the city of Los Angeles, up 1.7% from 2020, according to the latest count by the Los Angeles Homeless Services Authority.
Bass said she plans to announce a program to address homelessness called Inside Safe in the coming days. The plan, which Bass said will cost under $100 million, will be to use master leasing with motels to place unhoused people. She said her office has been in touch with motel owners near encampments.
Janice Hahn, chair of the Los Angeles County Board of Supervisors, said she plans to introduce a motion to make sure county resources can "match the urgency of this emergency declaration."
"We need to link arms rather than point fingers," Hahn said, adding that Bass was "bringing a new vigor to a battle that we have been fighting way too long."
Jennifer Hark Dietz, CEO of People Assisting The Homeless, said in a statement that Bass was right to declare a state of emergency.
"The city's approach to homelessness has become more piecemeal and politicized and this state of emergency can leverage the power of the executive branch to make sustainable improvements to our service system and dramatically increase the production of desperately needed housing," Dietz said.
The Committee for Greater LA, a group of cross-sectoral civic leaders, also agreed with Bass' decision in a statement from Chair Miguel Santana and Sarah Dusseault, chair of the group's housing and homelessness action team. The state of emergency allows for the city to better manage the use of city- owned land, expedite approvals for affordable housing and address the needs of people living in encampments, according to the group.
"Unprecedented actions, like those in Mayor Bass' plan, are needed to significantly improve the lives of people experiencing homelessness and to remove the barriers they face in securing housing," the statement read.