The 26-year-old, who is a Catholic, says she was forced out after refusing to have a church wedding.
She told The TES: "I was excited about getting married to the man I love and I thought I could talk to people about it. But then I was advised by a senior member of staff that if the school found out it was a civil wedding, there would be consequences."
The teacher at St Peter's primary in Cardiff, who asked not to be named, said that as a result of pressure from the school she even considered having two separate weddings.
When she decided just to have a civil ceremony her 12-month contract was not renewed, and another teacher was hired in her place.
She said: "I thought, I don't want to be in a position where I have to live two separate lives. I'm a Catholic, but I have issues with the faith. I was desperately unhappy.
"I don't know whether or not I want to teach any more. It was my dream job, but it turned into a nightmare."
She said she was twice asked to clarify her wedding plans when discussing extending her employment with Mike Flynn, the headteacher.
Mr Flynn admitted discussing the wedding but said his decision to let her go was based on "financial imperatives". He said the school often replaced teachers at the end of temporary contracts with cheaper, newly-qualified staff.
"These are legitimate and valid reasons. She's a very good teacher. Her contract wasn't renewed, but that's not unusual," he said.
Dr Elizabeth Edwards, chairwoman of the governors, said: "We are a Catholic school. Parents send their children to us to receive a Catholic education.
There is an expectation that all our staff support the mission statement of the school.
"It would be inappropriate to discuss the details of a contractual arrangement that existed between the governing body and any former employee with any third party."
The case comes at a time when there is concern over recruitment to RC schools. Schools are finding it increasingly hard to find devout staff. In June The TES reported that some diocesan education officers were privately calling for the church hierarchy to accept Catholic divorcees and others in "irregular" relationships who are currently barred from senior jobs.