At the request of the Trump administration, "the California National Guard will accept federal funding to add approximately 400 Guard members statewide to supplement the staffing of its ongoing program to combat transnational crime", said Brown in a letter to Homeland Security Secretary Kirstjen Nielsen and Defense Secretary Jim Mattis.
The Democrat said the California troops will not help build a wall or "detain people escaping violence and seeking a better life".
"Here are the facts: there is no massive wave of migrants pouring into California", the governor wrote.
It will take some time before Guard troops can be deployed.
Trump last week asked the governors of four southwestern states to deploy the National Guard as part of a plan to secure the U.S. -Mexico border against gang activity and illegal immigration.
Vehicles are parked April 10, 2018, at the U.S. -Mexico border fence in Calexico, Calif., that separates the city of about 40,000 from Mexicali, population 700,000, in the Mexican state of Baja California.
In his letter, Brown pointed out that the number of undocumented immigrants apprehended by Border Patrol agents is already the lowest its been in decades. And for days, leaders there had been tight-lipped about whether they would deploy National Guard troops. It says troops can not guard anyone in custody for immigration violations or participate in construction of border barriers. Overall immigrant apprehensions on the border last year were as low as they've been in almost 50 years (and 85 percent of the apprehensions occurred outside of California).
During an appearance on "Newsmax Now", Krikorian - the executive director of the Center for Immigration Studies - said people are misinformed about what the National Guard has the ability to do.
The Pentagon has said National Guard troops will not perform a law-enforcement role, and will be armed only for the goal of self-defense.
The California Guard program now employs 250 personnel, including 55 at the California border with Mexico.
The governor also noted that the state guard "agreed to similar targeted assistance" under the past two presidents.
He says another 112 of the 338 troops that Arizona has committed to Trump's operation will provide border air support, such as flying helicopters, from a base in the town of Marana near Tucson.