During the trial, the court had heard that on 2 September last year Mr Green had visited county hall to finalise arrangements for a meeting he was due to have the following week with Mr James to discuss land he co-owned at Travellers Rest near Carmarthen.
As he left he handed an envelope marked "private and confidential" to Mr James' personal assistant Liz Thomas.
When she opened it later in the day she found it contained £5,000 in £20 notes but there was nothing else inside.
Mr James called the chief constable of Dyfed-Powys Police and Mr Green was arrested that night.
Mr Green, a former dairy farmer who rents out properties in Llanelli, Kidwelly and Carmarthen, said the money was intended as a donation towards the refurbishment of Carmarthen leisure centre.
He said he was "indebted to the pool" because swimming lessons there had helped improve his children's' confidence, which had been hit while he and his wife were going through a divorce.
He accepted he had been "naive" in not leaving a covering note but had denied the charge of corruption.
"I made a mistake - I should have left a note," he told the jury.
The prosecution case had been that money was intended to "tempt" Mr James into looking favourably at Mr Green's plans for the land.
After more than four hours of deliberation the jury returned a unanimous not-guilty verdict.
I'm not surprised they acquitted. Millionaire property developers are renowned for their naivety.
Labour MP Andy Slaughter at the Khaybar Hatred March
12 hours ago