Yes. Aside from administrative liabilities, a lawyer may be jailed if he or she represents conflicting interests.
Under Article 209 of the Revised Penal Code, as amended by R.A. No. 10951, a lawyer “who, having undertaken the defense of a client or having received confidential information from said client in a case, shall undertake the defense of the opposing party in the same case, without the consent of his first client” shall be liable for Betrayal of Trust by an Attorney which is punishable by “prision correccional in its minimum period, or a fine ranging from Forty thousand pesos (P40,000) to Two hundred thousand pesos (P200,000), or both.”
Note that if the first client gives his or her consent then the lawyer may not be liable under Article 209.
Suppose the lawyer was appointed by the court as counsel de oficio for the second client (accused) without the consent of the first client (private complainant), is the lawyer liable under Article 209?
UberDigests submits that the lawyer may still be liable under Art. 209 because the only exemption cited there was if the first client gives his or her consent.
