Was playing with both hands ever allowed in chess? I was watching this video on Youtube of an Armageddon game between Vladimir Kramnik and Garry Kasparov which happened in 1995. It can be seen that Kasparov is using both of his hands for some moves. (For example, around the times 9:39, and 9:48)

My understanding is this is illegal.
 Why is it allowed here? 

Was this legal in the past? Or is it legal in any format of chess like Armageddon here?
Was playing with both hands ever allowed in chess?


Yes, before 1997. Hence in 1995 Kasparov was not breaking the rules.

The key article in the the FIDE Laws of Chess is:


  Article 4: The act of moving the pieces
  
  4.1   Each move must be made with one hand only.


This first appeared in the 1997 edition of the FIDE Laws of Chess.

The previous edition, in 1993, did not have this rule.