New Jersey Gov. Chris Christie (R) on Thursday appointed state Attorney General Jeff Chiesa (R) to fill deceased Sen. Frank Lautenberg's (D) seat until the upcoming October special election.

In his announcement, which came three days following Lautenberg's passing, Christie said he believes Chiesa is "the best person for the job."

"I have appointed someone who I have great faith and confidence in, and someone who I know almost as well as I know my own family," he said.

Lautenberg had suffered declining health for the past few months, and Christie indicated he had considered his options prior to Monday.

"I didn't just start thinking about this on Monday. I'd been thinking about it on and off for some time," he said.

Christie met with Chiesa and his wife Monday night to float the option, and Chiesa told him the next morning in a text that he would accept the appointment. 

He will not run in the upcoming special election, scheduled for Oct. 16.

His decision not to run leaves a wide-open Republican field for the seat. So far, only former gubernatorial candidate Steve Lonegan has announced his intentions to run for the Republican nomination. Former state Sen. Bill Baroni and state Sens. Tom Kean Jr., Michael Doherty and Joe Kyrillos are said to be considering a run as well.

But Democrats are heavily favored to keep the seat, so much of the focus on the race will be directed at the Democratic primary, which is expected to include at least three candidates.

Rep. Rush Holt (D) on Thursday became the first Democrat to officially announce his run. Rep. Frank Pallone Jr. (D) has been telling local Democrats he's running, and Newark Mayor Cory Booker (D) is collecting signatures to join the ballot.

Potential candidates must file 1,000 signatures by Monday.

Speaking with reporters after the announcement, Christie sought to assuage concerns that Chiesa would be beholden to the Republican governor during his short tenure in the Senate, with the upper chamber expected to take up significant legislation, most notably immigration reform.

"He's got a mind of his own," Christie said of the Senate appointee.

He said that the two hadn't discussed any specific legislation, but Chiesa did hint that he'll tack to the right on issues, calling himself a "conservative Republican."

On immigration reform, Chiesa said his top priority is border security.

“I think the first thing we have to do is make sure the borders are secure,” he said. “From there, these issues are new to me.”

Chiesa's appointment marks a rare occurrence for New Jersey, which hasn't elected a Republican to the Senate since 1972. It gives Senate Republicans an additional vote for the next four months, during what could be a pivotal legislative session.

Lautenberg died at age 89 of viral pneumonia on Monday. He was honored at a memorial service in New York on Wednesday, where Vice President Biden paid tribute to his legislative achievements, praising him as a man of “convictions.”

Lautenberg’s casket arrived in Washington, D.C., on Thursday where it will lie in repose in the Senate chamber before he is interred at Arlington National Cemetery.

This story was updated at 2:32 p.m.