Guillermo Iberio Ortiz Mayagoitia (born 10 February 1941) is a Mexican jurist and former Supreme Court Justice.

Ortiz Mayagoitia, a native of Misantla, Veracruz, earned his law degree at the Universidad Veracruzana in Xalapa.

He served the judiciary in various positions in Poza Rica and Tuxpan in his home state and as a clerk at the federal Supreme Court.

On 27 January 1995 his Supreme Court appointment, proposed by President Ernesto Zedillo, was ratified by the Senate.

He was elected Chief Justice, with seven votes out of eleven, by the Supreme Court on 2 January 2007.