Short answer. Yes, but only under specific conditions. Rule 130, Section 31 allows a conspirator's act or declaration to be used against a co-conspirator, but only if it was made in furtherance of the conspiracy and while it was still ongoing, and only after the conspiracy itself has been shown by evidence other than that statement.
What the law says
The act or declaration of a conspirator in furtherance of the conspiracy and during its existence may be given in evidence against the co-conspirator after the conspiracy is shown by evidence other than such act of declaration.
Rule 130, Section 31 — Admission by conspirator. Read the full provision →
Why this is an exception, not the general rule
As a general matter, one person's out-of-court statement cannot be used as evidence against someone else — that is the basic hearsay concern the rules of evidence are built around, and it protects an accused from being convicted on the say-so of another person he never had the chance to cross-examine. Section 31 carves out a narrow exception for conspiracies specifically, on the theory that when two or more people are jointly pursuing a common criminal plan, each conspirator effectively becomes the agent of the others for acts and statements made to advance that plan, so the ordinary hearsay wall does not apply in the same way.
Three conditions have to line up
The exception is not a blank check to admit anything a co-accused ever said. The statement must have been made "in furtherance of the conspiracy" — meaning it actually advanced the common plan, not just idle talk about it after the fact. It must have been made "during its existence," so a confession made after the conspiracy has already ended or been abandoned falls outside the rule. And critically, the conspiracy itself must first be shown by evidence separate from the statement being offered — the statement cannot be used to bootstrap proof of the very conspiracy that is supposed to make it admissible.
What that third condition protects against
That sequencing requirement exists precisely to prevent circular reasoning: if a co-conspirator's statement could be used both to prove the conspiracy existed and, at the same time, to be admissible only because a conspiracy existed, an accused could be convicted almost entirely on hearsay dressed up as an exception. Courts require the independent proof of conspiracy — through direct evidence, circumstantial evidence, or the conduct of the parties themselves — to come first, and only once that foundation is laid does the co-conspirator's statement become fair game against everyone shown to be part of the plan.