In Jane Austen's Pride and Prejudice, Mr. Darcy did indeed ask Mr. Bennet for his consent in marrying Elizabeth, as it was the necessary social custom in that time period, especially for a respectable, high-society gentleman like Darcy. Austen chose not to show us the scene between Darcy and Mr. Bennet; she instead chose to focus on the conversation Mr. Bennet has with his daughter after Darcy asks.
In Chapter 17 of Volume three Austen describes Mr. Darcy rising to follow Mr. Bennet to the library one evening after Darcy proposes to Elizabeth for the second time while walking towards the Lucases. Austen then proceeds to describe Elizabeth's nervousness, knowing what it is Mr. Darcy is asking her father. Next, Darcy returns from the library and whispers to Elizabeth that her father wants her in the library. Mr. Bennet tells Elizabeth that he has given his consent because Darcy is "the kind of man..to whom I should never dare refuse any thing" (Ch. 17, Volume 3). He also wants to understand why Elizabeth has accepted Darcy's proposal, wanting assurances that she really likes him and will be happy.
Mr. Darcy proposes to Elizabeth first and when she agrees, he asks Mr. Benett for his consent to let the two of them marry.