Lexical bundles are considered as one of the main rhetorical features in academic genres. The appropriate use of these features adds to the coherence and naturalness of the texts. Recently, genre analysis studies tend to investigate the similarities and differences across different academic disciplines and the effects of the first language of writers on the employment of these linguistic features. There are limited studies, however, in the field with a mere focus on the use of lexical bundles in PhD dissertations and the similarities and differences on the employment of these features among native and non-native English writers. In this regard, the current study, following a comparative corpus-based approach, investigated the use of lexical bundles in English PhD dissertations written by native English-speaking and non-native Kurdish-speaking writers across the two disciplines of biology and linguistics. All the compiled dissertations were selected from the ones published between 2010 to 2020 in British universities to keep the compiled corpora comparable. In the next phase, the distribution, linguistic structures, and functions of bundles used in introduction and literature review sections of the compiled dissertations were analyzed using WordSmith 6th edition concordancing software. The analysis provides a list of the most frequently used lexical bundles in each scientific field and among the two groups of writers. The structural analysis showed that noun phrases and prepositional phrases were the most frequently used bundles between both groups of writers and of disciplines. It was also found that passive structures were commonly used in biology dissertations. The functional analysis revealed that non-native Kurdish writers tended to use more research-oriented and text-oriented bundles in comparison with their native counterparts. It was suggested that the rhetorical differences and similarities between the two groups of writers and the disciplines could be attributed to the experience or proficiency levels of writers and the conventions, knowledge construction principles and research approaches of each academic discourse community. Pedagogically speaking, it is discussed that teaching discursive features and including language teaching tasks drawn from authentic texts such as text analysis tasks, focused tasks, extended writing tasks enable EAP learners to learn how to employ these linguistic features effectively to improve the flow of information, coherence and fluency in their academic texts.