Interlanguage variation has been found to be systematic and is conditioned by multiple linguistic, social and developmental factors. The present study was conducted to assess the effects of a set of linguistic, social and developmental factors on the past tense variable in L2 English in Macao. Past tense variation is prevalent among local speakers of L2 English in Macao, and is found even at high levels of L2 English proficiency. In Macao, English is substantially acquired and spread through education by non-native local speakers of English. Data collection thus targeted speakers who have a prominent role of spreading and influencing English locally. Based on 4058 past-reference verbs extracted from sociolinguistic interviews with twenty-two local English professionals and practising English teachers, the study shows that variation in past tense marking is highly systematic and subject to multiple linguistic, social and developmental factors. Moreover, it supports the universal constraints of verb saliency and aspect. VARBRUL statistical analysis of the data reveals that past tense marking by Macao-born speakers of L2 English is influenced by class of verb, lexical aspectual class of the verb, the preceding phonological segment, whether the preceding consonant is voiced or unvoiced, viewpoint aspect, age group, periods spent away from Macao in English speaking countries, education level and type of secondary school attended. The results for class of verb, lexical and viewpoint aspects indicate that locally born speakers of L2 English mark more phonologically salient forms, change-of-state verbs with clear results and aspectual perfectives. Verb saliency and aspect have been found to be universal constraints on past tense marking. These findings support both the Saliency Hypothesis and the Aspect Hypothesis and thus lend support to the universal status of verb saliency and aspect. The results for the effects of the phonological environments on [t/d] deletion show that a preceding obstruent favours [t/d] deletion, while a preceding nasal, lateral or vowel favours [t/d] retention and that a preceding unvoiced consonant favours [t/d] deletion and a voiced consonant favours [t/d] retention. In addition to linguistic factors, a set of social and development factors also constrain past tense marking. The results show that older speakers, speakers who had never been to any English speaking countries, speakers with higher education and speakers who attended an English medium school are more likely to mark verbs for tense than their counterparts are. The analysis reveals that past tense marking by Macao-born speakers of L2 English is highly systematic, conditioned by a set of linguistic, social and developmental factors. It also shows that variation in past tense marking is a consistent characteristic of L2 English in Macao. The present study serves as the initiation of the investigation of ‘Macao English’. It is encouraged that further variationist research on English used in Macao will follow.