I didn't use to study hard before I attended university.

[Mike MC]

Is the following sentence grammatical?
I didn't use to study hard before I attended university.

 

[PeterCW]

Source?

 

[Mike MC]

Source?

Actually, it's my own sentence when I was trying to say something similar to the following:
I wasn't studious before I went to university.

 

[Tarheel]

High school was relatively easy. I didn't have to study hard then, but now I do.

Something like that.

 

[Mike MC]

Actually, I finished university many years ago. The question is, can we use used to to talk about something you habitually had done before something else in the past? Do I need to change the original sentence to the following?
I hadn't used to study hard before I attended university.

 

[emsr2d2]

Actually, I finished university many years ago. The question is, can we use used to to talk about something you habitually had done before something else in the past? Do I need to change the original sentence to the following?
I hadn't used to study hard before I attended university.

That's very awkward. If you're determined to use "used" in this sense, say "I used not study hard before ...".

 

[jutfrank]

The question is, can we use used to to talk about something you habitually had done before something else in the past?

Yes, there's no problem with that in principle. You can talk about past habits before a point in past time.

Do I need to change the original sentence to the following?
I hadn't used to study hard before I attended university.

No, that's not right. You don't have to backshift. If you use the word 'before' in the other clause, the time relations will be quite clear.

Before I met my girlfriend, I used to cry myself to sleep.

 

[jutfrank]

I didn't use to study hard before I attended university.

This is the wrong verb. You need to mark a point in time. Here are four much better alternatives:

before going to university
before I went to university
before I started university
before university

 

[Tarheel]

Actually, I finished university many years ago. The question is, can we use used to to talk about something you habitually DID before something else in the past? Do I need to change the original sentence to the following?
I hadn't used to study hard before I attended university.

I didn't use to study hard before. Now I do.

If you are no longer going to college/university it would be more natural to say, "I didn't study hard before I started college/university, but I had to change my habits then." Something like that.