Jeremy Corbyn sacked a second senior figure for "disloyalty" and installed a Trident opponent in the key shadow defence brief as he sought to get a grip on his top team.
After more than 30 hours of apparently bitter wrangling, the Labour leader added Europe spokesman Pat McFadden to the casualty list alongside shadow culture secretary Michael Dugher.
Maria Eagle is being shifted from shadow defence secretary to replace Mr Dugher, having been seen as blocking Mr Corbyn's desire to oppose renewal of the UK's nuclear deterrent.
Her berth is taken by Emily Thornberry, who agrees with the leader on Trident.
Mr McFadden, whose place is being taken by Pat Glass, infuriated the leadership by criticising Mr Corbyn's response to the Paris terror attacks.
The MP said he had originally accepted the post because the EU issue was of "crucial importance" with an in-out referendum looming.
"Tonight Mr Corbyn has told me he does not want me to continue to serve on his front bench, in particular because of questions I asked about terrorism and national security in the Commons statement following the Paris terrorist attacks," Mr McFadden said.
"It is his prerogative to decide his front bench team and I will continue to support and work for Labour in any way I can."
He added: "I hope Labour retains its strong and clear position to campaign for the United Kingdom to remain in the EU."