Lautenberg died last Monday of viral pneumonia at age 89.
“I welcome Sen. Chiesa to the United States Senate,” Reid said ahead of the swearing in, which was preformed by Vice President Biden. “I congratulate him filling the seat. … I’m sure at some point I’ll get used to saying that name.”
Reid and Sen. Robert Menendez (D-N.J.) praised Chiesa's work as attorney general to prevent gun violence in New Jersey.
Chiesa has announced that he will not run in the upcoming special election, scheduled for Oct. 16.
The swearing in of Chiesa came ahead of key legislative work in the Senate. He was sworn in just one hour before the Senate votes on a large five-year farm bill. Later this month, the Senate is also expected to vote on comprehensive immigration reform.
"Even though it's only five months, I'm sure he will make a mark here on the Senate," Menendez said.