I purchased my Mac Pro towards the end of 2012. I have done regular software updates and am wondering just how long this laptop will be supported by Apple before it bombs out. What is the lifespan of this laptop?

What do you mean by "bombs out" exactly? A computer does not just stop working simply because its no longer supported by its manufacturer.

Also support can be in 2 forms, Hardware through service, and software through OS updates.

Currently 2012 MacBook Pros will support the upcoming macOS Catalina, but that will likely be the last major macOS update for them.

That does not mean they will instantly stop working the moment a new macOS update is released. Apple will continue to issue security updates and fixes for previous macOS versions for at least 2 years after they have been superseded.

So for a 2012 MacBook Pro that means you'll get Catalina this year, and then software fixes at least until 2021.

After that the computer will continue to work as it has but no longer receive any software updates, and App support from 3rd party developers may start dwindling.

Whether it still does what you need at that point, is entirely up to you to decide. But at around 10 years old by then, it seems like a decent life span for a computer.

A Mac Pro is not the same as a MacBook Pro. You need to be clear when asking questions here.

It depends upon how you perceive lifespan. I have used a 17 year old computer that met my needs. Some people consider a computer that can't be upgraded to the latest operating system as near-useless and a major security risk.

Notebooks tend not to last as long as old desktops, but with a 2012 model at least you can replace some parts unlike new computers where when one small thing fails you pretty much end up spending a lot or just buying a new model.

So if you want specifics we need specifics. According to https://www.apple.com/macos/catalina-preview/

you will be able to install the newest macOS but how well it runs may depend upon other features of your hardware.

What screen size? The 2012 non-Retina 13-inch model stayed in the line for over four years, and did not go out of production until Oct 2016. Therefore, per Apple's stated policies, it has parts and service support until Sept 2021 in most places. The 15-inch version of the non-Retina 2012 went "vintage" (no more parts/service support) in Sept 2018. The Retina 2012 models also went vintage in 2018.

For understanding "vintage' and "supported," please see this Apple article:

Vintage and obsolete products - Apple Support

2012 models support the upcoming macOS version, Catalina, so you should be good for a while.