Jose Luis Cota, 50, a 15-year veteran of the border agency, also submitted a resignation letter.
His plea in San Diego federal court comes a week after his two co-defendants, Mexican nationals Miriam Juarez Herrera and her husband, Gilberto Aguilar Martinez, admitted their roles in the smuggling scheme.
The conspiracy started in November 2015, with Juarez agreeing to recruit immigrant clients to be smuggled in her vehicle and Cota waving them through his lanes at the port of entry while he was on duty, according to the plea agreement. He admitted to allowing Juarez to smuggle at least 10 immigrants.
Aguilar admitted in his guilty plea last week to handling the transportation of the clients once they had crossed the border, reuniting them with family in the U.S. and collecting the smuggling fees.
The clients were charged as much as $15,000 each for illegal entry, Cota's plea stated. That fee sometimes included providing the client with fake identification for the crossing, provided by Juarez.
In one instance, Cota admitted, he received $13,000 after allowing two immigrants to cross illegally in a vehicle. He also agreed in the plea that the government could prove he had deposited more than $44,000 in bribes into his bank accounts while he was under investigation.
Federal agents from the FBI's Border Corruption Task Force seized more than $17,000 in bribes when they searched Cota's home in September, the U.S. attorney's office said.
Cota has agreed to forfeit all of the bribery money.
The trio were arrested in September — Cota at his workplace and the couple during a traffic stop after a smuggling incident.
The task force began investigating Cota in 2013 after an immigrant reported that she and Cota flirted as he was returning her back to Mexico in 2011. They ended up meeting later in Tijuana and their conversation turned to how he could smuggle people across the border, according to a search warrant.
Investigators said Cota married a Mexican woman whom he had processed as she was being sent back to Mexico in 2010. He tried to obtain a visa for her to live in the U.S. legally but it was denied, and she continued to live illegally in the country, the search warrant said.
Cota is set to be sentenced April 7. He could be sentenced to at least five years in prison.
"Public corruption, which includes border corruption, is the No. 1 criminal priority for the FBI because of the potential harm that actions, like Officer Cota's actions, can have on our nation's security," Eric Birnbaum, special agent in charge of the FBI's San Diego division, said in a statement.