Humberto Llanos Martínez was the 18th Mayor of the commune of Pichilemu, office which he held for two three-year terms, between December 1935 and May 1941.

He took office following the death of the previous mayor, Serafín López Lizana, and was succeeded by Felipe Iturriaga Esquivel.

The mayor-elect was Serafín López Lizana, and his council was composed of the regidores Alberto Morales Moraga, Ramón Klehmet Genoux, Felipe Iturriaga Esquivel and himself.

However, López Lizana died in office just four months later, in September, and Llanos Martínez was elected mayor by the council in December of that year.

Llanos was re-elected mayor, this time popularly, for the 1938–41 term; his council for that term was composed by Lorenzo Arraño Ortíz, Carlos Silva Prado, Vicente Richard, and Alberto Morales Moraga.