Peter Mohan Maithree Peiris, PC (Sinhala: පීටර් මොහාන් මෙෙත්‍රී පීරිස්) is a Sri Lankan lawyer and diplomat.

[3] Following his schooling, Peiris entered the Sri Lanka Law College for his legal studies and was called to the bar on 19 June 1975 as an Attorney-at-law and became a Solicitor of the Courts of England and Wales in 1978.

[3] During this time he was trained at the National Institute of Trial Advocacy of the Harvard Law School, at the Centre for Police and Criminal Justice Studies of the Jesus College, Cambridge and at George Washington University.

[6] He withdrew murder charges in a case against former deputy minister Chandana Kathriarachchi and served an indictment on unlawful assembly for which the accused pleaded guilty.

[11] Peiris was nominated to be Chief Justice by President Mahinda Rajapaksa following the controversial impeachment of Shirani Bandaranayake.

[24][25] The International Commission of Jurists condemned Peiris' appointment, describing it as a "further assault on the independence of the judiciary".

According to Sirisena, Mohan Peiris visited him several times begging not to remove him and promising to deliver judgements according to his wishes.

[1] Peiris was appointed the Permanent Representative of Sri Lanka to the United Nations in January 2021 by President Gotabaya Rajapaksa.