I will make sure to ask her first before doing anything.

[Talab1234]

1. I will make sure to ask her first before doing anything.

2. 1. I will make sure that I will ask her first before doing anything.

Are both sentences grammatically correct?

 

[emsr2d2]

1. I will make sure to ask her first, before doing anything.
2. 1. I will make sure that I will ask her first, before doing anything.

Are both sentences grammatically correct?

With the addition of the comma, as shown above, they're both grammatically correct. However, neither is particularly natural. A native speaker would say something like "I'll be sure to ask her before I do anything".

Please note that I've changed your thread title. Titles must be unique and relevant to the thread, and include some/all of the words/phrases/sentences you are asking us about. Titles such as "Sentence - grammar" (your original) are useless here - they could apply to thousands of posts.

 

[jutfrank]

It's not exactly clear in what context you imagine this to be uttered. If you want to reassure the person you're speaking to that you will ask her, I suggest this:

I'll make sure I ask her first before doing anything.