The move is more evidence that lawmakers in the nation’s most populous state, where Democrats hold two-thirds majorities in both houses of the legislature, are girding for possible court battles after Trump takes office on Jan. 20.
Last month, leaders of both houses introduced bills to protect undocumented immigrants from anticipated efforts by a Trump administration to increase deportations.
In addition, Democratic Governor Jerry Brown has made combating climate change a priority for the state.
“Mr. Holder and his team will serve as outside counsel to the Legislature, advising us in our efforts to resist any attempts to roll back the progress California has made,” Kevin de León, the Democratic leader of the state Senate, said in a statement.
A representative from de León’s office could not immediately be reached for comment.
Holder served as attorney general under President Barack Obama from 2009 to 2015. He is a partner in the law firm of Covington & Burling, which represents companies and helps them navigate government regulations.
“I am honored that the Legislature chose Covington to serve as its legal adviser as it considers how to respond to potential changes in federal law that could impact California’s residents and policy priorities,” Holder said in a statement.
California voted decisively for Democrat Hillary Clinton in the Nov. 8 presidential election, choosing the former first lady over Trump by 28 percentage points.