Biden, Democratic National Committee Chairwoman Debbie Wasserman Schultz and Minneapolis Mayor R.T. Rybak called a former Edward Kennedy staffer also named Marty Walsh instead of the mayor-elect.
Biden started to congratulate Walsh before realizing he was speaking with the wrong person.
"You son of a gun, Marty!" he said on the phone. "You did it!"
Apparently, the two Walshes have been dealing with this mix-up for years.
"We've had this for the past 20 years happening back and forth. Marty tells a funny story from 2006 when Kennedy thanked me from the stage and his mother thought it was for him," non-mayor-elect Walsh told the Cape Cod Times.