He said he was subjected to comments about his sexuality and dress style, while workers claimed he was having a homosexual relationship with a colleague.
The man, who did not wish to be named, said staff told him the only reason he got the job was because his father was a member of the board.
He said this made the atmosphere very unwelcoming after he got the job in 2008.
The worker said an assistant manager made comments about his "camp" accent and told staff not to ask him for help with IT issues, although he was the contact person for these queries.
The officer worker said he overheard conversations between board members in which one man asked if he was gay, which was followed by laughter. He said the man said: "I had better not be left alone in a room with him. I hope it's not contagious."
The office worker said he was so upset, he went to the toilet to compose himself, but was afraid to make a complaint in case he lost his job.
He said a colleague told him that he had heard another staff member refer to him as "one of them, a queer, like".
The worker said a female colleague referred to him constantly as "one of the girls", while other colleagues made insulting comments about his dress and manner. He said one colleague often made comments like "do you like taking it up the back passage?"
The worker said he was aware there were unfounded and hurtful rumours that he was in a homosexual relationship with the credit union's treasurer.
He said he felt constantly on edge at work and physically sick due to the harassment.
Although he made a complaint to management, they did not address the harassment or bullying at a meeting, he claimed.
He said they claimed he had taken a company laptop and one manager thumped the table, and threatened him with legal action.
The man said the laptop had been given to him instead of a salary increase or bonus.
He said he made a formal complaint but there was no investigation, but he got a letter to say there were not sufficient grounds to back up his grievance.
The credit union denied that it treated him badly because of his sexuality, or that there was a homophobic atmosphere in the office.
Colleagues denied they made discriminatory comments.
An Equality Officer found that the credit union discriminated against the man as he was harassed on the grounds of his sexual orientation.
It awarded him €8,000 in respect of the discrimination, and €16,000 in respect of the victimisation he suffered.
The man's solicitor said he wished to remain anonymous during the case, and was not willing to comment because the employer still had time to appeal the result.