Mr Mwamba, who is popularly known as GBM made the announcement during an impromptu Press conference at his residence in Kasama, the provincial headquaters of Northern Province yesterday.
He cited the impasse between Government and the Bemba Royal Establishment as the reason behind his resignation.
Mr Mwamba told journalists who had gathered at his residence that he had been given an ultimatum by the Head of State to choose whether his allegiance lay with him as President or with Paramount Chief Chitimukulu-designate, Henry Kanyanta Sosala.
He said that looking at the history he had with the Patriotic Front (PF) as a party and Mr Sata, he felt the President had put him in an awkward position by asking him to take sides.
“Naumfwa kwati bamfutatila,” he said in Bemba meaning he felt like the President had turned his back on him.
The ultimatum follows hot on the heels of a visit he paid with his wife Chama to Chief Chitimukulu’s town house on Sunday evening.
During the visit, he pledged to continue supporting the embattled traditional leader who has outstanding issues with Government over his succession.
Mr Mwamba, who himself is a member of the royal family and is closely related to Mr Sosala whom he refers to as his grandfather, said he could not turn against the paramount chief-designate as he was a blood relation.
He said when President Sata received information of his visit to Mr Sosala’s home, the Head of State gave him an ultimatum to choose between being a member of his Cabinet or aligning himself with Mr Sosala.
“I received a call from George Chellah (Special Assistant to the President for Press and Public Relations). I don’t know what he meant by calling me on George Chellah’s phone, but I picked up and Chellah said hold on for the President. When I spoke to him, the President asked me why I lied that he had sent me to see the Chitimukulu.
“The President then said ‘you and Chanda Sosala don’t speak for me. The OP (office of the President) has told me that you went to say I had sent you,” Mr Mwamba said.
He said he explained to the President and vehemently denied uttering any words to that effect as allegedly reported by intelligence officers that were present during his visit.
State House, however, said it had not received any official notification of Mr Mwamba’s resignation.
This is according to a statement issued by Mr Chellah as monitored on Zambia National Broadcasting Corporation television main news last night.
Mr Chellah said President Sata would take further action on the matter once he was notified officially.
The Kasama Central parliamentarian said he had earlier requested for representation from the intelligence service for clarity over the purpose of his visit.
“My former commander-in-chief, however, said ‘I don’t trust you…I trust the OP’ when I am a member of his Cabinet and Minister of Defence for that matter. Well, what could I do, he is my boss,” Mr Mwamba said.
This is the second time Mr Mwamba has resigned. In September 2010, Mr Mwamba temporarily resigned his position as Kasama Central MP.
Mr Mwamba said he had resigned to concentrate on his business which he claimed had been affected because of his involvement in politics.
This was after PF president Mr Sata, then in the opposition temporarily, relieved Mr Mwamba of his position as party chairperson for elections.
This followed the assault and wife battering charges levelled against him.
Quoting more snippets from his conversation with the President, Mr Mwamba said he was told that Cabinet decisions were made collectively, especially after Tourism Minster Sylvia Masebo brought up the issue of the standoff between Government and the Bemba Traditional Council during one of the meetings.
He, however, said he would not be part and parcel of a collective decision that would affect his family.
“So we continued talking with the President back and forth and he said well, it’s entirely up to you. Choose between Henry Kanyanta Sosala and your job.
“So here I am now, I have chosen Kanyanta Sosala because he is my grandfather. It is for this reason that I have decided to resign as Minister of Defence with immediate effect. I will still remain a Member of Parliament (MP) for Kasama Central, but if they so wish that I should also step down as MP I will come back to you and consult you so you can advise me on what I should do,” he said.
He thanked the President for according him the opportunity to serve in Government.
During his visit to Mr Sosala’s home, Mr Mwamba said he and Minister of Finance Alexander Chikwanda had declared interest in the issue surrounding the appointment of Mr Sosala as Paramount Chief Chitimukulu of the Bemba speaking people because he was their relation.
Before resigning, Archbishop of Kasama Ignatius Chama was seen arriving at Mr Mwamba’s home where the duo discussed the events leading to the resignation.
Insiders said the clergyman tried to dissuade Mr Mwamba from resigning but to no avail.
Others seen at the residence were Lubansenshi MP Patrick Mucheleka and Home Affairs Deputy Minister Alfredah Kansembe.