The assessment of the interpreting quality of simultaneous interpreting within legal sphere is a daunting task, particularly if carried out between two different varieties of two different languages. The present paper seeks to examine the interpreting quality of simultaneous interpreting of a legal speech from Jordanian Arabic into formal English. The paper uses quality assessment model as both a theoretical framework and a research tool with its four criteria: accurate rendition of the ST, adequate TT expression, equivalent intended effect and communicative interaction process alongside a semi-structured interview. The paper argues that multiple interpreting issues have emerged during the interpreting process; some of which, like inappropriate use of terms, errors at all levels, contradiction, speed and density of information, etc., have impacted the interpreting quality of the interpreted legal speech as they have affected the message content. Contrariwise, certain interpreting issues have arisen during the interpreting process without affecting the interpreting quality of the interpreted legal speech, such as addition, change of focus, omission of discourse markers, grammatical transposition, etc. This paper offers a baseline for interpreting quality assessment of simultaneous interpreting of a legal speech between two different varieties of Arabic and English using quality assessment model and semi-structured interview, which may have implications for examining interpreting quality of simultaneous interpreting in similar simultaneous interpreting quality assessment contexts.