A teenage husband and wife who allegedly expressed a desire to become a "jihadi Bonnie and Clyde" have been charged with planning to carry out a terrorist act in Sydney.

Sameh Bayda and his wife Alo-Bridget Namoa, both aged 19, face a maximum penalty of life in prison after their charges were upgraded on Wednesday to conspiring to carry out a stabbing attack in Sydney in late 2015.

Sameh Bayda is already facing terrorism charges. Credit:Nine News

The pair have been in custody since they were arrested early last year in Guildford.

At that time, Mr Bayda was charged with three counts of collecting documents likely to facilitate terrorist acts.