Past studies have found that the linguistic experience of previously-acquired languages, such as one’s native-language (L1) and second-language (L2) learning experience, modulates the perception of novel sounds from a third language (L3). Lexical tone in L3 is a good case for testing the influence of L1 or L2, as listeners with varying language backgrounds may use different pitch cues (pitch contour or height) in tone perception. The present study focuses on L2 learners of Mandarin whose L1 variety is either Seoul Korean (SK), a non-tonal stressless language, or Gyeongsang Korean (GK), a tonal pitch-accent language. Intermediate-to-advanced SK-speaking and GK-speaking L2 learners of Mandarin were recruited as target groups, and naive listeners of respective L1 varieties were recruited as control groups. The participants completed an AX forced-choice tone discrimination task. Four Cantonese tones, one rising tone and three level tones, were used. Contour–level and level–level tonal contrasts were target tone pairs, allowing for testing the primary use of pitch contour and pitch height, respectively. The results showed that the two groups of naive listeners had greater accuracy in discriminating level–level than contour–level tonal contrasts. In contrast, L2 learners, independent of their L1 varieties, showed higher accuracy in discriminating contour–level than level–level tonal contrasts. The L2 learners’ perceptual pattern is consistent with Mandarin listeners, as reported in previous work. Taken together, the findings provide evidence for a possible developmental change in which Korean-speaking L2 learners might have a perceptual cue shift from pitch height to pitch contour through their L2 experience in Mandarin. The findings about the role of L2 proficiency in Mandarin further supported the effect of L2 experience on learners’ increased use of pitch contour.