The former leader of Lincolnshire County Council, Ian Croft, has been banned from being a county councillor for 15 months.
Mr Croft denied he wanted revenge on his colleague
The Standards Board of England and Wales found he had breached the code of conduct for people in public office.
Its panel heard Mr Croft wanted revenge after colleague David Bowles testified against previous leader, Jim Speechley, who was jailed for misconduct.
The board found he had consistently undermined Mr Bowles in the media.
'Lack of trust'
It also found he had failed to support Mr Bowles on several occasions.
In December 2003, with the investigation into Speechley well underway, Mr Croft wrote to council solicitors asking for Mr Bowles' contract of employment to be terminated.
In 2004, after time off with stress, Mr Bowles was contacted by council solicitors who ordered him not to return to work. He disregarded this notice.
Shortly after this Mr Croft was asked why he was trying to get rid of Mr Bowles.
He replied: "Because of a lack of trust and confidence."
Mr Croft was found to be in breach of a total of nine counts relating to the code of conduct demanded of people in public office.
Mr Speechley was jailed for 18 months in 2004 for misconduct in public office, relating to his influencing the route of a bypass.
Then chief executive Mr Bowles gave evidence at the trial and was seen as a 'whistleblower'.
He left the county council the same year, saying his job had become impossible.
Mr Croft resigned as leader in March 2005 after a damning Audit Commission report but was re-elected as a councillor in May.
After the hearing Mr Croft said he had no comment but added it was unlikely he would appeal against the ban.