Yes, it's a dependent clause—and, because it's going first, there should be a comma after it.

From ["Commas with Subordinate Clauses—A Reader’s Question"][1] at The Editor's Blog, Beth Hill says the following:

> **An adverbial clause often starts with a subordinating conjunction.** A short list of subordinating conjunctions:

>       although  
>       after  
>       as  
>       because  
>       before  
>       once  
>       since  
>       though  
>       until  
>       when  
>       while

> **A subordinate clause that stands alone is a sentence fragment . . .** While we can use dependent clauses as sentence fragments, most of the time we don’t. We usually pair them with at least one independent clause and create sentences . . . Independent clauses often come first in our text, but putting dependent clauses first gives us variety in sentence construction . . .

> When an adverbial dependent clause comes *before* the independent clause, we put a comma after the dependent clause (between the clauses). We don’t have to give any consideration to the topic of essential or nonessential—**when the dependent clause comes before the independent, use a comma to separate them**.

---

Note that it's a dependent clause because it wouldn't make sense on its own *unless* it were in response to what somebody else said:

> "As a member of the rescue team."  
> "Sorry, what?"

      *but*

> "In what capacity did have a terrifying experience?"  
> "As a member of the rescue team."

In short, in order for it to be meaningful in any way, it has to have context—either within a dialogue or linked to an independent clause in the same sentence.

  [1]: https://theeditorsblog.net/2014/07/30/commas-with-subordinate-clauses-a-readers-question/