～というのは事実（じじつ）だ is a phrase used to strongly express that (A) is something that is ‘true’, ‘a fact’, or has ‘no doubt’. というのは may be used after almost any phrase, before the 名詞（めいし） 事実（じじつ） ‘truth’, paired with the 助動詞（じょどうし） (auxiliary verb) だ
) will determine that phrase to be a fact.
It is a fact that this person killed my mother.
It is a fact that she is a lawyer.
The literal translation というのは事実（じじつ）だ
is ‘that which is (A) is true’, as (A) is just a nominalized phrase. It is also quite common to see this expression with という omitted, the only difference being that it sounds slightly weaker.
It is true that I ignored the red light.
It is a fact that I worked it out with my girlfriend.