Research has shown that collaboratively produced texts are better in quality compared with individually written texts. However, no study has considered the role of collaboration in authorial voice, which is an essential element in current writing curricula. This study analyzes the effects of collaborative task performance in the quality of L2 learners' argumentative texts and in their authorial voice strength. A total of 306 upper-intermediate L2 learners were selected and divided into independent (N = 130) and paired (N = 176) groups. Each learner/pair was asked to write one argumentative text. The quality of writings was determined by a quantitative analysis that included three measures of complexity, accuracy, and fluency (CAF). Participants' authorial voice strength was assessed by two raters using an analytic voice rubric. Comparison of means revealed that pairs outperformed independent writers in all CAF measures. However, the results for the role of collaboration in authorial voice were mixed: While pairs were more successful than independent writers in manifesting their ideational voice, independent writers outperformed pairs with regard to affective and presence voice dimensions and holistic voice scores. The article concludes that, despite its positive implications for L2 writing, collaborative writing may pose challenges for learners' authorial stance taking.