Just want to know if there has ever been a case where a tech-prist has gone on to become an Inquisition or is it unheard of

Firstly, No (but they do become Throne Agents still).

Secondly...

To quote from Ascension (pg. 29, black box) under The Adeptus Mechanicus and the Inquisition:

"The doctrines and dogmas of the Cult Mechanicus demand that the servant of the Omnissiah surrender not just everything he owns, but everything he is and everything he could otherwise have been. The rites of the machine change not only the initiate's body, but also his mind and very soul. It is a route from which there is no return, for once the glory of the Monissiah is revealed to a Tech-Priest, every other strand of faith and every other callling seems frail and hollow. As the Tech-Priest's limbs are augmented with prosthetics of iron, so is his brain matter replaced with silicon. However, despite these physical changes, it is the soul of the Tech-Priest that is altered the most. The truths of the universe revealed unto him are so terrible that without the protective Rites of the Omnissiah, his soul would be shattered. Although the Quest for Knowledge might take him into regions of thought and deed many would proclaim as heretical, it is to the Omnissiah, in all its forms, that the Tech-Priest owes his deepest allegiance.

So all-encompassing is the Quest for Knowledge, so total a Tech-Priest's surrender of mind, body, and spirit to the Omnissiah, that he may never espouse any other calling or creed. He may not therefore become an Inquisitor, an Interrogator, or a devout memeber of the Ministorum, for each of these makes equally stringent and mutually exclusive demands on his being."

The class or belief doesn't mean the Tech-Priest doesn't stand a chance of acquiring the status anyway. The issue is that it's **** near impossible to maintain that sort of status and still call yourself a Tech-Priest (or Inquisitor) as the requirements to maintaining both will back you into a Sophie's Choice where you will, ultimately, have to determine where your loyalties lie and probably get hunted down by the Inquisition for a general heresy or by the Adeptus Mechanicus as an Omnissian Apostate. Remember that the Adeptus Mechanicus is the other eagle head on the Aquila, they are an empire-within-an-empire and their autonomy is only second to the Inquisition in how they go about the business of THEIR Adepta and they have their own agents to hunt down hereteks. I assume, to avoid a shadow (or real) war between the two Adepta, that the Inquisition just doesn't try to poach from the Mechanicus as the risks are nowhere near worth the gains to be had.

Thirdly, yes...

The Radical's Handbook features an Inquisitor called Cyrrik Scayl, who has originally been a Tech-Priest Magos from Hadd (Lathe Worlds).

Cyrrik Scayl is a Throne Agent formerly of the Ordo Hereticus, but he is (or, in this case, was) no more an Inquisitor as Seraph or Kane is in that same section.

It seems to me that a tech priest would never be completely trusted by the Inquisition enough to be given the position of Inquisitor.

Ultimately, tech priests owe their allegiance to the Adeptus Mechanicus, which is some ways is autonomous from the Imperium. Furthermore, tech priests are what many within the Inquisition and Ministorum would consider heretics. I think that inquisitors would view the elevation of a tech priest to Inquisitor as losing their power to a separate and somewhat questionable faction within the Imperium.

I am sure i saw one art made by John Blanche, one of the oldest ilustrators or WArhammer, in a Warhammer 40000 artbook , portraying one Tech marine Inquisitor. I remember it because was awesome! Maybe should be very difficult for the Inquisition to trust the Adeptus Mechanicus, since both institutions are so secretive, but i believe should not be impossible, after all, an inquisitor benefiting both factions, is a boon for both of them. Maybe if such individual exist, must be distrusted, and probably work alone or mostly with other tech marines and even rogue traders, and i see it as an Ordo Xeno representative, and Hereticus or even a malleus is too difficult to grasp for the machine probably.

Even saw an art of a female magus, i believe.

Female tech priests are just as common as males, they choose people by their level of competence, not sex.

dosan said:

Possibly this is the "magus" you're speaking about?

Urgh. I hate Blanche's artwork.

Interesting concept though.

Yes, that is the female tech priest! Awesome!