Would it be ok/wise to end my PhD contract after submitting my PhD thesis in order to be able to start a new job at that time? I would like to start looking for a job in the period preceding the submission of my thesis, so that if I’m lucky and I find a job, I could end my PhD contract (around PhD submission time) and take on that job. 

I am asking because my PhD contract allows me to remain employed until my defense date (already fixed). During the time between the submission and defense (around 2.5 months), since the work expected to be done during my PhD is already done, I would be spending this time doing tasks I’m not interested in, just to fill this gap. The thing is I’d rather spend this time working on something new with a new employer. 

Worth noting is that in our lab there is a history of other students ending their PhD contracts at early stages or mid-way (for different reasons) but not at an advanced stage, like I’d like to do. 

Are there other considerations I should take into account if I do something like this (Besides the risk of being unemployed if I’m not lucky enough to find a new job) ?
It is entirely common for students to take on a job before they have formally completed the program, and then do the defense and submit their thesis in the coming months. It happens all the time, and everyone understands that if you have a job offer that you intend to take and can't defer for a couple of months, then you should of course take the job. Employers will also understand if you tell them up front that you will want to take a couple of days of vacation early on in your tenure at the company to travel back to your university to defend your PhD.

So, yes, it is ok to do what you propose.