Andrelle Leedham was warned he faced a lengthy sentence after being convicted of masterminding the plot to get contraband into Featherstone Prison.
Warder Hannah Stewart aged 27 had fallen for the 26-year-old father of one while he was locked up in the jail for blackmail, Stafford Crown Court heard.
Prosecutor Mr Gerard Quirke told how the pair met in the education department where the 27-year-old operational support officer worked and explained: "He showed her a lot of attention, exercising the charm he undoubtedly has."
Recorder Peter Cooke said he believed the lovers had sex in prison despite Stewart maintaining they were not intimate until after Leedham was released in August last year. The sexual relationship fizzled out within a couple of months but they remained in contact and the defendant hatched the drug plot by text message, the court was told.
Stewart from Oaks Drive, Featherstone, whose father and brother have both been prison officers at the jail, has admitted her involvement in the drug plot and misconduct in a public office. Her father had been the 'personal officer' for Leedham while the defendant was held at the prison but knew nothing of what his daughter had been up to, the court heard.
Recorder Cooke said after the jury unanimously fond Leedham guilty of conspiring to supply cannabis and anabolic steroids and conspiracy to convey a prohibited article into HMP Featherstone: "I do not accept that the defendant threatened her over the conspiracy. It is my belief that he inveigled his way into her affections and was manipulative towards her. But in my view all he was threatening to do was to turn up on the doorstep of her family and announce what had been going on, which would not have gone down well with her father and brother.
"There is no evidence that this was anything other than the first consignment they had attempted to bring into the prison. But of the four defendants Leedham was the prime mover and was certainly pulling the strings.You must expect an immediate custodial sentence of some length."
Leedham from Thompson Avenue, Blakenhall was remanded in custody and will be sentenced with the two inmates also involved in the plot at a later date. Stewart, who is on bail, will learn her fate at a separate hearing.