President Trump on Sunday named Mark Morgan as the head of Immigration and Customs Enforcement, calling him a “true believer and American Patriot.”

Mr. Morgan, a career FBI agent who served as border patrol chief in the last six months of the Obama administration, was tapped to replace acting director Ron Vitiello, who resigned last month after Mr. Trump said he wanted to go with someone “tougher” on border security.

“I am pleased to inform all of those that believe in a strong, fair and sound Immigration Policy that Mark Morgan will be joining the Trump Administration as the head of our hard working men and women of ICE. Mark is a true believer and American Patriot. He will do a great job!” Mr. Trump tweeted.

I am pleased to inform all of those that believe in a strong, fair and sound Immigration Policy that Mark Morgan will be joining the Trump Administration as the head of our hard working men and women of ICE. Mark is a true believer and American Patriot. He will do a great job! — Donald J. Trump (@realDonaldTrump) May 5, 2019

The decision comes with the Trump administration undergoing a shake-up on border security that includes the resignation last month of Homeland Security Secretary Kirstjen Nielsen.

Mr. Morgan has championed the Trump administration’s call for a border wall and emergency declaration. He defended the president last month when he said more families are coming because they know they will no longer be separated, calling it “like Disneyland.”

“What happened? The president is correct. The numbers of family units skyrocketed. They have been trained and educated — grab a kid, come in, you’re going to be allowed into the United States,” Mr. Morgan said on Fox News.

He also advocated for ending “catch-and-release” by fixing the 1997 Flores settlement, which in effect prevents most migrant children from being detained for more than 20 days after crossing the border illegally, but said he wasn’t optimistic about the prospects of congressional action.

“Congress has shown again and again their failure to do what’s right. Again, they want to eat the elephant again in one bite, instead of looking at what they need to do right now,” Mr. Morgan said.

Matthew Albence currently leads the agency as ICE acting director.