Martin Garrix

In this video, it can be seen on the studio computer at 11:56.

In a studio session video, Martin Garrix said he uses different versions of FL Studio he has installed, since he has not consolidated all the samples and synth sounds into one version (due to lack of time).

The official Image Line website features a Martin Garrix testimonial:

I looked for a program that is easy to use for productions and gives fast results when making tracks. I tried to switch to logic a few times but it's just not my thing. If I have an idea I want to be able to work it out really fast so I can decide if it's worth finishing. Besides that FL Studio has some really good plugins itself which I use a lot.

A few more sources:

• In this video Martin Garrix In The Studio With Future Music, at 1:40 and throughout, a very clear shot of him using FL Studio can be seen.
• He can also be seen using FL Studio throughout this Martin Garrix Masterclass at ADE Sound Lab XL 18.10.17 @ DeLaMar Theater.
• On Feb 17, 2017 Martin Garrix uploaded a "Behind The Scenes" video of his single Scared To Be Lonely which he made with Dua Lipa. He can be seen working in FL Studio, which you can get a clear shot of if you pause at 1:37.
• At 2:47 of the official video for Glitch, you can see on his laptop that Garrix is using FL Studio.

[In response to being asked what he uses to produce] "@Pabdelatorre95 fl studio and a bit of logic sometimes"

At 1:13 of the video "Martin Garrix Goes Undercover on Twitter, YouTube and Reddit | GQ," on Quora he is asked:

Which software does Martin Garrix use?

He answers:

I use FL Studio, and to record vocals we use Pro Tools. FL Studio is just an extension of my brain. If I think of something, it takes me 30 seconds before its in there. It might not sound good, but the idea is there… and then afterwards I polish it.

His actual answer on Quora can be seen as a comment to this question here.

8:13 "Well, um... to be honest I started with Garageband."

At 8:38 in the video "HOW WE MADE 'USED TO LOVE' | The Martin Garrix Show S4.E4" on YouTube, it is visible that Audacity is pinned on Martin Garrix's laptop taskbar, confirming his use of the software.