Henry Bolton has refused to step down as Ukip leader after facing a wave of pressure from within his own party to resign.
It comes after a number of resignations from his frontbench team, with those quitting their posts demanding that he steps down.
Mr Bolton insisted he would fight on, despite the vote of no confidence in his leadership by the party's national executive committee (NEC).
He hit out at the NEC which he said needs "significant and urgent reform".
Speaking in Kent on Monday, Mr Bolton said: “I respect the next steps in the constitutional process and will therefore not be resigning as party leader.”
He added: “Instead, during the next four weeks I shall be calling for the coordination and mobilisation of all Leave campaigns, to ensure that the Government delivers full independence from the European Union in all areas of Government and administration, and I shall be calling for the party itself to mobilise to support this agenda.
“This is the most pressing matter facing our country and I am determined not to allow the NEC to distract the party away from participating forcefully in the Independence debate.”
The party’s assistant deputy leader Mike Hookem MEP, local government spokesman Tim Aker and education spokesman David Kurten were among those to announce they had quit their posts.
Deputy leader Margot Parker, immigration spokesman John Bickley and international trade spokesperson William Dartmouth have all also stepped down, demanding Mr Bolton resigns.
Mr Bolton did not take questions after the announcement, made in Folkestone, Kent.
In his brief speech outside a hotel, he added: "It is now time to put an end to the factional in-fighting within the party and to remove those who have been a part of that.
"In a single Phrase, it is time to ‘Drain the Swamp’."
