The centre-left Dostour (Constitution) Party's spokesperson Khaled Dawoud resigned late Saturday after the higher committee accepted party head Hala Shukrallah's resignation.
Dawoud said in a statement that he had intended to resign two months ago following the election of a new party president.
Those elections were postponed and Dawoud remained in his position.
The resigned spokesperson added that due to Shukrallah's resignation and the fact that the elections were postponed, he decided to resign.
On Saturday, the party's higher committee accepted Shukrallah's resignation.
Shukrallah, who was elected last year, is the first Coptic woman to be elected as head of an Egyptian party.
She cited internal divisions threatening the party as her reason of quitting.
Party secretary general Tamer Gomaa will take over as acting president until elections are held.
Dawoud, who had been the party spokesperson for three years, stated that he hopes elections for a new president will take place soon.
Elections for president, secretary general, and treasurer were supposed to take place 8 May but were postponed to June, and then 28 August, and will be postponed again following the resignations.
Dawoud also stated that he hopes the party will protect its cohesion.
Founded by opposition figure Mohamed ElBaradei in 2012, the Constitution Party has seen disagreements over the timing of internal elections, who is eligible to vote and to run, and whether the party will participate in the parliamentary elections due to take place before the end of this year.
The party had announced in February that it would not participate in the parliamentary elections.