It’s available in English in its original form, drawn by ONE, on OneWebComic - the translated version of the web comic is fairly complete, but the website its hosted on periodically drops several, or sometimes several dozen, of the older episodes (I’m guessing it’s based on hosting fees or something) but the more recent chapters seem to be pretty consistently available. The webcomic is years ahead of the Anime, and several months ahead of the redrawn version of the Manga by Murata Yuusuke.
ONE’s uniquely expressive drawing styles are crude, but very much responsible for the final action and the look and feel of what Murata Yuusuke creates. Here’s an example:
The published version of the Manga, drawn by Murata Yuusuke, is also available in fan-translated English, albeit a few years behind the web comic. Here’s a sample of what Murata Yuusuke creates with the inspirations of ONE’s original illustrations:
If you haven’t experienced One Punch Man, or if you’ve only watched the Anime, check out the manga. It’s delicious cake.
Just a heads up - one of the curious things of the relationship between ONE and Murata Yuusuke is that after the redrawn chapter appears it sometimes disappears and gets completely redrawn. Sometimes ONE objects to something Murata Yuusuke did, or Murata Yuusuke decides that he didn’t quite capture the motion in the chapter well.
Either way, you’ll sometimes read the same chapter “JUST RELEASED” three or even four times before the final version comes out.
For me, that’s a bonus, because I enjoy watching the artists working on “What we meant to say instead” and improving the chapters, and the redrawn chapters often are significant improvements, so it’s all good.