The candlelight vigil will honor those killed in the Newtown, Conn., school shooting last December, said Sandra Ruliffson, president of the Brady Campaign Contra Costa County chapter, which is organizing the event.
The gathering will begin at 6:30 p.m. outside City Hall at 100 Gregory Lane, and will include a bell-ringing.
The group has joined with other local organizations, such as political advocacy group MoveOn, to support President Barack Obama's call for Congress to pass stricter gun laws, including universal background checks for those who want to purchase firearms, an assault weapons ban and limits on high-capacity magazines.
"We know that people are really upset with what happened and they want change," Ruliffson said.
Twenty children were shot and killed in the shootings at Sandy Hook Elementary, along with six adults.
The shooter, 20-year-old Adam Lanza, also killed his mother at her home, and took his own life.
She said the tragedy has spurred people in Contra Costa County to get involved politically.
"There will be people for whom this is the first time they will be participating in something like this," she said.
Ruliffson said tonight's vigil and rally will show that all sides are coming together to keep communities safe.
"We know that most people that are longtime gun owners do support sensible gun legislation," she said.
Pleasant Hill Mayor Michael Harris and representatives from the office of Congressman George Miller, D-Concord, have been invited to attend, Rulffson said.
After the names of those killed in Newtown are read, attendees will have an opportunity to share stories of those affected by gun violence locally.
"The impact of gun violence ... it's so pervasive," Ruliffson said.