Q: Can I submit a journal paper based on my thesis that is not yet published?

It is quite a popular practice to publish parts of one’s thesis as journal articles. However, a journal article has to be an original work that has not been published anywhere before. Therefore, a lot depends on where and in what form your thesis is being published. Generally, when universities publish thesis papers, they print out copies of it and circulate it internally. In such cases, the thesis is not considered to be formally published, and this will not affect your journal article in any way.

However, if the thesis is published by a serious academic publisher and made publicly available, then there could be a problem. In that case, you should ensure that the journal article is published before the thesis, that is, by Jan. But if, due to some reason, the journal article publication is delayed, and the paper gets published after the publication of the thesis, then there might be a problem. 

Therefore, it is advisable to inform the editor at the time of submission that your article is based on your thesis, mentioning the tentative publication date of the thesis. It is always better to clarify such things at the beginning rather than face allegations of misconduct later. Additionally, you should remember that a thesis and a journal article are two completely different sub-genres of academic writing that cater to different audiences and set different expectations. You should take the basic idea from your thesis and rewrite it in the form of a journal article. You should cite the thesis in the article. To well understand the requirements of a journal article and how it differs from a thesis, you can take guidance from a senior colleague or your supervisor.