Supt David Borrie, of Northumbria Police, is said to have simply been told "don't apply for promotion" by his chief constable, Mike Craik.
Mr Craik has been at the centre of allegations about officers' conduct.
The claim was made at a tribunal brought by the force's former head of legal services.
Denise Aubrey, 54, was sacked in 2014 for gross misconduct after allegedly disclosing information about an affair Mr Craik was said to be having with his assistant chief constable, Carolyn Peacock, and a second relationship between two further high-ranking officers.
Mr Aubrey denies she did so and is claiming unfair dismissal, sexual and disability discrimination, victimisation and harassment.
In her witness statement, she said Mr Borrie, who is now 57 and retired from the force, pursued the "extremely vulnerable" civilian member of staff, who cannot be named for legal reasons, and "groped her in the office".
She said: "On another occasion, he took her for a drink in the afternoon at a pub and then pressurised her into giving him oral sex."
This happened a second time and eventually an investigation was launched, the tribunal in North Shields heard.
Ms Aubrey said: "Whilst it was felt that a criminal charge would not succeed, he had clearly breached police standards.
"Instead, it was decided to move him but to allow him to complete his service so that he could get his pension. Mr Craik decided to have a 'quiet word' with him and told him 'not to bother applying for promotion'.
"However, the IPCC [the police watchdog] insisted that he received a formal written warning."
Earlier in the week, the tribunal was told Mrs Peacock's husband, who was also a policeman, punched Mr Craik at a barbecue after learning of the affair.
Officers were called to deal with the altercation, but the record of the incident was then said to be deleted - leading to an allegation of a "cover-up" by Ms Aubrey's QC, Daphne Romney.
Rumours of the relationship began circulating in 2007, Ms Aubrey said.
Allegations of a second affair at the force, involving assistant chief constable Greg Vant and Mr Craik's secretary, Juliet Bains, were also raised at the tribunal.

Remus Hamza, 40, is alleged to have attacked the woman near Cardiff University as she walked home alone on 20 September last year.
The prosecution at Newport Crown Court has alleged she was so drunk she could not have consented to sex.
The defendant, who is Romanian and lives in Cardiff, denies rape.
Mr Hamza told Newport Crown Court she smiled and "kissed him back" near the Civic Centre but did not say anything.
Speaking through an interpreter, Mr Hamza said: "This girl was looking at me, laughing at me, smiling and I thought she was smiling at me because she liked me and I just grabbed her backside.
"She just smiled at me and laughed... she came with me without me having to force her in any way.
"If she didn't want to have sex with me that night she could have just have said no."
He admitted the woman was intoxicated but claimed she had been "aware of herself".
He said he didn't tell police about the "consensual sex" in his first interview because he was embarrassed and had been advised by a solicitor to give no comment.
The court was told Mr Hamza pleaded guilty to exposure in a similar area in 2014.
A policeman who pressured a vulnerable member of staff into two sex acts was allowed to keep his job so he would not lose his pension, a tribunal heard.
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A man accused of raping a 20-year-old woman in Cardiff during fresher's week said she "could have just have said no" to his advances, a court has heard.