The bass player joined the 'Enter Sandman' group in 1986 to replace Cliff Burton - who had died in a road accident - and left in 2001 after relationships between the band members broke down.
However, Jason insists it was his decision to exit which benefited the band and helped them carry on.
He said: ''I don't know if this is selfish, and anybody can take it the way they want, or maybe it's egotistical - I'm not sure - but I truly feel that I saved [Metallica] in 1986 by being the right choice [to replace Cliff] and being able to take all the s**t.
''I also saved their band 12 years ago by stepping aside and letting them carry on with what they wanted.''
He explained: ''I was not able to be on the same page with them anymore, they were taking too much time away from the band. We hadn't plugged in our amps for months and months and months by the time that I had made the decision and called the meeting to talk to them.''
Jason now plays in his own project, Newsted, and admits he started venturing into his own plans after his fellow musicians stopped putting Metallica first.
Speaking to Blabbermouth.Net, Jason said:''There had been so much distraction from actually playing the metal that I couldn't take it anymore. I was busy with my other project - I already started recording. I was already going forward with another project that I was gonna do a worldwide release with, because they weren't spending any time playing any music.
''I always put Metallica first. When those guys stopped putting it first all the time - like we all used to do together - it changed things for me. They weren't able to give the same amount of time to play at volume and remember why we were doing this.''