The fast-growing practice of e-commerce implies a strong increase in parcel deliveries, which in turn creates significant pressure on last-mile city logistics. Due to the important role the city transportation plays in energy use and greenhouse gas emission, effective last-mile solutions in cities must be developed to contribute to sustainability and a cleaner world economy. Crowdsourced delivery as an emerging “sharing economy” initiative can be an effective tool to mitigate the problems emerging from the last-mile city logistics. To valorise the benefits of crowdsourced delivery, a transition towards a hybrid city logistic system is required where crowdsourced delivery and the conventional delivery networks are closely integrated. Due to the lack of theoretical guidelines for crowdsourced delivery integration, this research develops a conceptual framework to facilitate last-mile city logistics transition adopting the multi-level socio-technical transition theory as the basis. The core of the conceptual framework is the “five basic principles” to be followed by stakeholders when designing intervening niche innovations at the current stage of system transition. To demonstrate the usability of the conceptual framework, an illustrative discrete event simulation study with specific settings that fits in with the current status of last-mile city logistics is conducted. Results show that incorporating crowdsourced delivery as a supplement to the conventional delivery network, following the five basic principles proposed by the conceptual framework can reduce the last-mile logistic costs. Moreover, the offline participation rate plays a key role in ensuring the feasibility of the new hybrid last-mile model. To conclude, the developed conceptual framework has a great potential of improving last-mile delivery in the era of e-commerce and having a critical scale of potential deliverer pool is the prerequisite for the successful application of crowdsourced deliveries.