I painted my fireplace a year ago and since then, I've received several questions about how I did it. I've intended to do this for a while, but tutorials can be a little time consuming so I'm sorry its taken so long but here it is.
Here's what I started with before we moved in. The bricks look like they were recycled, but mostly they were still so dark and depressing and that's not the least bit appealing in a basement room.

I hated the fireplace and mostly tried to just pretend it wasn't there. I just thought that someday we'd just pay to reface it with stone, have it removed or
something. Then, one day I thought of all the days I drove home from work through a certain neighborhood admiring the old homes. Some homes were brick and had been painted. Some of the painted brick homes had weathered paint and, some looked like some kind of chalking had given an uneven white appearance to the brick like on the house below. These houses were the ones I loved the most.

Inspirational lightbulb moment.
I loved this on the exterior of a house so why not on a brick fireplace wall?
Make no mistake. I'm normally gung-ho for paint projects but I was truly afraid to do this. In the house where I grew up, I watched my dad spend years stripping layers and layers of paint (red, white, blue) from a brick fireplace probably 1/4 of the size of mine so I knew that once I put a paint brush on that brick, it would be forever. Ultimately, I decided that if it went wrong, I could just paint it all out completely and I could live with it because I'd rather have a stark white wall over the dark hole it was. After I made peace with my decision, I went for it.
All I needed was semi-gloss white paint that I had on hand and a 2.5" brush. I have an angled brush pictured below and it will do the job fine but if you have the square type, its probably better. I did not paint the grout - Brick only.
Now, on to the details (on sample bricks):
~ Don't put too much paint on the brush at one time. I dipped the tip of the brush into the paint and wiped off a good portion of the excess.
You do not want too much paint. Starting out, I would suggest using less paint until you get the hang of it and find the right amount that works for you but keep in mind that less is more here. Too much paint and you're going to end up with a solid white brick or a glob. You can also come back later if you want to add more. This is the perfect amount ...
~
Next, brush across the brick, without putting too much pressure so that you get semi-even paint across the brick but you aren't getting solid coverage.
Then brush up and down blending out any brush strokes.
Its okay if its uneven because randomness is what you're going for. There is no exact science to this and it doesn't have to be perfect, but you also don't want it to be an obvious glob of paint or brush strokes. Don't worry about perfection.
This part is important! ~ Step away from the wall every few bricks.
Take a step away from the wall and see how it looks overall. The appearance of your work is going to look different up close than it will standing away from it when you look at an entire section of bricks and your technique will change without your ever realizing it. In the photo above, for example, there's what I think an obvious horizontal paint glob that I would blend more. I didn't notice this standing so close. When I worked on my wall, I found myself slowly adding more paint as I went across the wall and taking a step back helped keep things even.
This may sound scary and complicated. It really isn't. I actually think its easier than painting a solid wall because you aren't cutting in, doing trim or striving for perfection like when you paint a wall. Its been a while since I did it but I think it took about 90 min. for me to do the entire wall.
I know many people are anti-paint on brick and I completely understand that, but if you're like me and really hate it, its your house and you should make it something you love. I hope this helps for anyone out there considering this project.