Translation check

ENG: I need to submit the homework tomorrow. So, I have to complete it by tonight.

JAP: 明日宿題を必要提出する。そこで、今日の夜までには完成する.


Thank you.

"Need to" do something requires some work.

For the first sentence:
明日宿題を提出しないといけない。
明日宿題を提出する必要がある。

For the second:
今日の夜のうちに完成しないといけない。
今日の夜のうちに完成する必要がある。

2nd :
今日の夜 is 今夜(こんや/kon-ya) usual.
Also 今日の夜のうちに is 今夜中(こんやじゅう/konya-jyuu)に may better,
but "(period)中に" is "while/for (period)" usual if exam.
"by (period) = まで(に)" is basically corrcet.

And "complete" is just "全て(or全部)終わらせる(subete/zenbu owaraseru : finish all)"
also"全て(or全部)片付ける(subete/zenbu katazukeru : clean up all)" possible.
なので(orだから)、今夜中に全て(or全部)終わらせなければならない。
なので(orだから)、今夜中に全て(or全部)片付けなければならない。

完成させる is not incorrect but just using make/build a something by hand or tools case usual.
Ｉf a important report written over a long period is using "complete/完成" better as included "at last/ようやく、やっと、".
If for regular homework "終わる/片付ける" enough.

To Satomic,

I tried to provide suggestions with minimum changes to the Original Poster's translation, so that he could rely on the words he's used, and still focus on the "need to (do something)" expression :)

I don't think there's anything wrong with そこで、

Also, you can say 今日の夜までには if it's still daytime. までには which means "until (it becomes nighttime)" means that you haven't reached that point yet. In other words, it is not yet 夜. So if it's still daytime, you can say 今日の夜までには
The reason I'm mentioning this is because you can use "by tonight" even if it's still daytime.

On the other hand, if it's already nighttime (夜), you have to use expressions such as 夜のうちに or 今夜中 which mean "within (tonight)".

Just my 2 cents.