Clinton will rely heavily on her tenure as secretary of state and will "speak extensively" on why she believes Trump is unqualified to be commander-in-chief, Sullivan said.
The speech, which kicks off a five-day swing through California ahead of next week's primary, will be an extension of the argument Clinton often makes on the trail: A Trump presidency would cause unrest and be dangerous for Americans.
Clinton will also spell out why Trump "is unlike any presidential nominee we've seen in modern times and he is fundamentally unfit for the job," Sullivan said.
Clinton has already given several national security speeches since launching her campaign last year — on the Iran Deal, ISIS and following the terrorist attacks in San Bernardino and Brussels.
Although Clinton is still battling Vermont Sen. Bernie Sanders in the remaining primary states, her campaign speeches have shifted to focus on Trump almost entirely.
A large portion of those remarks lately has been dedicated to Trump's foreign policy comments, most often criticizing his proposal to temporarily "ban" Muslims from entering the United States and his suggestion that the United States should pull out of NATO.
That was the case on Wednesday during a New Jersey rally where Clinton said: "I gotta tell you, I think that Donald Trump has disqualified himself completely" before detailing his various national security plans.
On Thursday, the Clinton campaign said, voters can also expect to hear her rebuke Trump on his past positions on nuclear weapons and torture.
"You will hear in her speech a confidence in America and our capacity to overcome the challenges we face while staying true to our values — a strong contrast to Donald Trump's incessant trash-talking of America," Sullivan said.
Clinton is locked in a tight battle for the Golden State, with a new NBC News/WSJ/Marist poll showing her in a virtual tie with Sanders. Clinton, along with her husband and former President Bill Clinton, will barnstorm California ahead of Tuesday's contest.
This story originally appeared on NBCNews.com.