He was born into a medium landowner noble family, which originated from Zala County, as the only son of György Rajki (died before 1494) and Katalin Osgyáni.
She married Gotthárd Sitkei, castellan of Pápa who participated in the suppression of György Dózsa's peasant revolt.
Since the 1510s, Rajki involved as a lawyer in numerous lawsuits in different parts of the country, which fact confirms his professional status.
For instance, he defended the interests of the Zagreb chapter against George of Brandenburg before the court of Petar Berislavić, Ban of Croatia in 1517.
The Szaniszlófis' defense team was initially led by another famous contemporary lawyer Gergely Makrai, and subsequently directed by Rajki, while Ferenc Fancsikai represented the Perényis.