Scott Kilday walked out of MJM International when he found a listening device hidden within artificial flowers.
The bug had been been set-up amid fears Mr Kilday was planning to quit to work with Mone's ex-husband Michael - and that the lingerie tycoon listened to recordings.
Mr Kilday - who had the role of Operations Director at MJM - eventually took the firm to the an employment tribunal. He had claimed unfair dismissal and also argued that he had been denied thousands of pounds in shares.
Following a hearing in Glasgow last September, judges found in favour of the 35 year-old in respect of the claim of unfair dismissal but lost his claim for £25,000 on the shares issue.
In a written judgement, MJM's decision to plant the listening device was likely to "destroy or seriously damage" Mr Kilday's trust in his bosses.
Mr Kilday was awarded £15,920 in compensation as a result.
The tribunal was previously told how matters became "difficult" with the lingerie firm after Mone split with her husband and business partner Michael in December 2011.
Mr Mone eventually left MJM days after another firm - MAS Holdings - bought into the business in February last year.
Mr Kilday, of Glasgow, said around that time Mone asked him to resign as a director.
Mr Kilday said he was "not particularly pleased" and "sought legal advice".
He also told how Mone had been "a very difficult person to work with" and that his relationship with her had latterly been "tense".
He then set up talks with Eliaz Poleg - chairman of the firm following the sale.
But, just days before the meeting, Mr Kilday found a listening bug in his office.
Recalling the shock find, he explained: "It was by chance more than anything else. We actually had a tanning product at the time and just in front of the plant pot I had samples of this product.
"They were sitting there not in a particularly tidy state. This day when I looked over they were in a tidy state - I found this very unusual.
"I went over, had a look in the pot and seen a cable coming out, which was wrapped around artificial flowers."
Asked by his lawyer John MacMillan what his reaction was, Mr Kilday told the tribunal he was "horrified" and left the company.
The hearing was told the device had been hidden for "business strategic reasons" and had been authorised by Mr Poleg.
Mr Poleg gave evidence and said he made the move due to "extreme concerns" over Mr Kilday's loyalty to the lingerie firm.
Mr Poleg told the tribunal: "I know there was stuff on it because Michelle said she was listening and replacing the tape machines.
"Michelle listened to these machines. Michelle advised me two separate times she heard Scott speaking about leaving the company.
"She said she heard him speaking to Michael Mone. She heard him saying: 'I'm going to leave the company shortly'."
It emerged during the hearing that Mr Kilday now works for Mr Mone's firm Pendulum Apparel.
MJM contested the unfair dismissal claim.
In written findings, the tribunal panel said had MJM could have "legitimately taken steps" to "protect its business interests".
Employment judge Shona MacLean went on: "The fact...that a recording device was placed in his office was in the tribunal's view conduct likely to destroy or seriously damage the degree of trust and confidence an employee is entitled to have in his employer."
She said by hiding the bug, Mr Kilday could "not be expected to put up with it."
A spokeswoman for Ultimo Brands International said: "We are delighted to have won the main aspect of this case relating to the shares of £25,000. With regards to the secondary case, we are in discussions with our lawyers and insurers to review our options to appeal."