Despite communicative language teaching’s popularity in many countries, including Canada and America, empirical studies that shed light on practical communicative language teaching and assessment (CLA) of L2 writing are scarce. Therefore, this study opted to contribute to teaching and assessing L2 writing literature from the Communicative Language Teaching (CLT) perspective. First, a Writing Communicative Competence (WCC) rubric was developed drawing on Bachman and Palmer’s (1996, 2010) language testing model, and then, it was pilot tested following a concurrent triangulation mixed-methods design. Six teachers and six learners from a language school in Montreal rated two written samples using the rubric (quantitative component) and responded to an open-ended questionnaire that elicited their opinions about the rubric and their experiences using it. Following the recommendations of teachers and students, the WCC rubric was revised. Second, an intervention study was carried out to explore the effect of communicative competence strategy training using the WCC rubric on L2 writing performance. Twenty intermediate-level participants were divided into two groups: the control group (n = 10) and the experimental group (n = 10). The control group received regular instruction for eight weeks. In addition to regular instruction, the experimental group participated in four explicit strategy training sessions that targeted raising participant’s awareness about writing communicative competence: 1) the teacher explained the components of the WCC rubric and how to use it; 2) the teacher modeled how to apply the rubric to writing and how to assess essays using the rubric; 3) the learners, in pairs, analyzed written samples using the rubric; 4) the learners wrote their essays, assessed their peers’ essays, and revised their essays using the rubric. Twenty-eight raters rated essays that were collected on the pre-test and the post-test and responded to a questionnaire. The results indicated that the WCC rubric is a reliable and useful teaching and assessment tool for L2 writing.