Nadia Whittome said she has been advised by her doctor to take several weeks off for her health to improve.
The Nottingham East MP said the decision was “incredibly difficult” and one she feels “very sad” about.
In a statement, Ms Whittome, 24, said she has been battling “some persistent health issues” over recent months.
“Until now, I have been attempting to manage them alongside continuing with my full-time work as an MP,” she said.
“Unfortunately, it has become clear that this is not feasible and I have been advised by my doctor that I need to take several weeks off in order for my health to improve.
“I feel it is important for me to be honest that it is mental ill-health I am suffering from – specifically post-traumatic stress disorder (PTSD).
“Through being open about my own mental health struggle, I hope that others will also feel able to talk about theirs, and that I can play a small role in creating greater acceptance and facilitating healthier discussions around this issue.”