No
==

Because of the same reason an indestructible car will still crush you to a pulp in a high-speed crash.

The human body is not very good at accelerating/decelerating quickly, or absorbing impact. If the Knights decide to repeatedly stampede you with cavalry, you will die. If they decide to dance around you while attacking you with maces, you will still die. The diamond armor may not even suffer a scratch, but it won't absorb the impact for you either.

If they decide to rope you with steel chains, you can't do much either. Even with a diamond sword, it takes a lot of time and effort to sever a steel chain. And I don't think the sword will do much good if you are being dragged behind a galloping horse. All they have to do is drag you to a cliff and throw you off. You will die a glorious death in a diamond armor!

Not to mention that hardness and strength are very different properties, as [Philip Rowlands][1] points out in [his answer][2].


  [1]: http://Philip%20Rowlands
  [2]: https://worldbuilding.stackexchange.com/a/54331/195