The President of the New Jersey Senate will become acting governor should there be a vacancy in both the governor and lieutenant governor positions pending a special election. The current Senate president is Steve Sweeney.
Prior to 2010, New Jersey had no lieutenant governor so Kim Guadagno is the inaugural holder of the office. She was elected in 2009 and re-elected last November as part of Christie's ticket.
Prior to 2010, when the position of governor was vacant, the president of the New Jersey Senate became acting governor. He or she continued to serve as the Senate president and as a state senator while simultaneously serving as acting governor. If he or she were to resign as Senate president, he or she would have also losing the acting governorship as it was an ex officio role.
The constitutional amendment that created the post of lieutenant governor basically put the new post right after the governor in the line of succession but otherwise kept the rest of the line of succession intact.