The mistrial is a blow to the Justice Department, which has been investigating Menendez for nearly five years, and will be a sigh of relief to Democrats worried about possibly losing his Senate seat to Republicans.
Menendez said he felt vindicated.
"I want to thank the jury, 12 New Jerseyans who saw through the government's false claims and used their Jersey common sense to reject it," he told reporters outside the courthouse before blasting the Justice Department.
"The way this case started was wrong, the way it was investigated was wrong, the way it was prosecuted was wrong, and the way it was tried was wrong as well," he said. "Certain elements of the FBI and of our state cannot understand or, even worse, accept that the Latino kid from Union City and Hudson County can grow up and be a US senator and be honest."
Menendez also had harsh words for those who predicted his political doom.
"To those who were digging my political grave so that they could jump into my seat, I know who you are, and I won't forget you," he said.
Prosecutors did not immediately announce whether they will refile charges against Menendez.
"The Department of Justice appreciates the jury's service in this lengthy trial," DOJ spokesperson Nicole Navas said. "The Department will carefully consider next steps in this important matter and report to the court at the appropriate time."
McConnell wants Senate investigation
Any delay in refiling charges at this point helps Democrats who want to hold onto his Senate seat and virtually eliminates any realistic possibility that Republican Gov. Chris Christie -- who leaves office on January 16, 2018 -- could select the senator's replacement if he were to resign or be removed from the Senate.
But shortly after the verdict, Senate Majority Leader McConnell, R-Kentucky, called for a Senate Ethics Committee investigation.
"(Menendez) is one of only 12 US senators to have been indicted in our history," McConnell said. "His trial shed light on serious accusations of violating the public's trust as an elected official, as well as potential violations of the Senate's Code of Conduct."
Menendez faced charges of conspiracy, bribery, and honest services fraud related to allegedly abusing the power of his office that could carry decades in prison. Prosecutors say the senator accepted more than $600,000 in political contributions, a luxurious hotel suite at the Park Hyatt in Paris, and free rides on a private jet from a wealthy ophthalmologist, Dr. Salomon Melgen, in exchange for political favors.
Both men deny all charges.
Defense lawyers argued that Menendez and Melgen were longtime friends with no corrupt intent to commit a federal crime, and after over two months of testimony, prosecutors never produced a smoking gun in the form of a document, email or incriminating phone call outlining an illicit agreement between the two men.
The seven-woman, five-man jury initially told Walls it was deadlocked Monday after several hours of deliberations. They reported back Thursday that they remained unable to reach a verdict. One juror, Ed Norris, told reporters the jury was split 10-2 on all counts in favor of acquittal.
Judge William Walls declared the mistrial after interviewing all 12 jurors.
"I find that you are unable to reach a verdict and that further deliberations would be futile and there is no alternative but to declare a mistrial," he said.
The trial -- which stretched on for 11 weeks -- included 57 witnesses and hundreds of exhibits, but the central factual allegations were never in dispute.
"This case really isn't about what happened," Lowell told jurors during opening statements. "It's all about why it happened."
Prosecutors relied mostly on circumstantial evidence to prove their case -- spending the opening weeks of trial painting a jet-setting lifestyle of the rich and powerful before ultimately turning to the "official acts" they argued Menendez did to help his friend.
They accused Menendez of pushing officials to help resolve an $8.9 million Medicare billing dispute in Melgen's favor, while the defense team claimed at trial that the senator was focused on the fact that the billing policies at issue were conflicting and the drug companies were enjoying a windfall.
Similarly, when several State Department witnesses testified that Menendez has threatened to hold a congressional hearing if they did not intervene in a contract dispute between Melgen and the Dominican Republic over cargo screening at the nation's ports, the defense said that the senator was troubled by port security more generally.
Last week, a juror excused for a long-planned vacation to the Bahamas telegraphed the divisions in the jury room and predicted a mistrial.
"It's going to be a hung jury," said Evelyn Arroyo-Maultsby, who told CNN she would have voted to acquit on all charges if she had stayed on the jury. "I know there's a few that feel the same way I do, and they're going to hold their own."