I'd like to say "I introduced Mary to John" but only really know how to use 紹介する when talking about a single person. Is に the correct particle to use in this situation?
For example: ジョンにメリーを紹介しました。
I think the most basic form is:
Ａが Ｂに Ｃを 紹介した。
A introduced C to B.
Of course, you don't have to include all three. In your example, the subject is implied:
私がジョンに メリーを 紹介しました。
(I) introduced Mary to John.
The word order is fairly flexible, as it usually is in Japanese, and some other variations are possible, but the basic answer to your question is that yes, に is the right particle, marking an indirect object.