Learn French: Depuis qu'il travaille ici, il est plus heureux. - Since he has worked here, he is happier.

We are currently learning to use the future tense after time words like quand and dès que. Why doesn't depuis que use the future tense here?

Words like quand (when) and dès que (as soon as) trigger the future tense when you are describing an event that hasn't happened yet. However, depuis que (since) describes an action that has already started and is currently ongoing, so it doesn't point to the future. Instead, it takes the present tense.

Why is travaille in the present tense when the English translation says 'has worked'?

In French, when an action started in the past and is still happening right now, you use depuis or depuis que combined with the present tense. English uses the present perfect ('has worked') or present perfect continuous ('has been working'), which is a very common trap for English speakers learning French!

Could I just say Depuis il travaille ici instead of Depuis qu'il?

No, because depuis by itself must be followed by a noun or a time phrase (like depuis lundi or depuis 2015). When you want to follow it with a full clause containing a subject and a verb, you must add que to make it depuis que. Because il starts with a vowel, que drops its 'e' to become qu'il.

How does plus heureux translate to 'happier'?