He announced the move in a long and slightly bizarre letter to President Trump, and the internet has been having a field day with the news.
He'd also previously said it was up to God to protect the environment.
But others are concerned that his temporary replacement - coal lobbyist Andrew Wheeler - won't be a much better defender of the environment.
Of course, there are also plenty of people just laughing at the whole thing while the world burns around us, because what else is there to do?
These are the most important and also the funniest responses so far.
Scott Pruitt resigned and 3 poachers got eaten by lions.— God 🌈 (@TheGoodGodAbove) July 5, 2018
Today was a good day.
This may be a controversial take but I'm not sure replacing Pruitt with a coal lobbyist is a huge upgrade— Judd Legum (@JuddLegum) July 5, 2018
Breaking: Trump to name leaking barrel of pesticides to replace Scott Pruitt as head of EPA. pic.twitter.com/AuN8HDSyyb— The Hoarse Whisperer (@HoarseWisperer) July 5, 2018
2/ For one thing he was one of the most corrupt cabinet members in history, and Congress did nothing.— Phil Plait (@BadAstronomer) July 5, 2018
4/ And third he should be in prison, not roaming the country able to do more damage. THAT would make me happier.— Phil Plait (@BadAstronomer) July 5, 2018
BREAKING: Scott Pruitt becomes first U.S. cabinet official to ever resign via epic poem pic.twitter.com/0YYJbixXDW— Rex Huppke (@RexHuppke) July 5, 2018
Scott Pruitt probably stole the pen he signed his resignation letter with.— m i t h (@ManInTheHoody) July 5, 2018
We have caught Scott Pruitt leaving Washington! pic.twitter.com/oz2TGHSe5d— Muckmaker™ (@RealMuckmaker) July 5, 2018
There are 16 investigations into Scott Pruitt's behavior and dealings and they weren't enough to push him out, but one woman confronts him at a restaurant and days later he's out.— Denizcan Grimes (@MrFilmkritik) July 5, 2018
Hold them all accountable in public, everywhere, every time. No limits.
Scott Pruitt has resigned to focus more on his true passion, throwing uncut plastic soda rings into the ocean.— OhNoSheTwitnt (@OhNoSheTwitnt) July 5, 2018
Scott Pruitt's resignation letter teaches 2 things:— Mrs. Betty Bowers (@BettyBowers) July 5, 2018
1. The # of times someone reminds you how religious they are in business letters is directly correlated to how much you need to check petty cash after they go.
2. Saying God gave you a job, you were unethical at, is blasphemy. pic.twitter.com/Lo26v9k05u
Patriotic Americans hope Scott Pruitt is somewhere toasting his service with a BPA-full plastic cup of Flint water— Faith Salie (@Faith_Salie) July 5, 2018
Just because Scott Pruitt resigned doesn't mean we've forgotten about the taxpayer funds he's misused or the damage he's done to our environment. We must have someone running the EPA that will protect clean air and clean water.— Kamala Harris (@KamalaHarris) July 5, 2018
Let's hope that whatever comes next, it's better for us and our living planet than Pruitt.