In this paper, we unveil the Software-Defined Low Latency (SDLL) framework based on Software-Defined Networking (SDN) to provision the Quality of Service (QoS) and guarantee ultra-low latency in 5G and beyond Transport Networks (TN). SDLL aims to tackle Time Sensitive Networking (TSN)’s weaknesses by providing agility and flexibility in terms of Traffic Engineering (TE) and Queue Management (QM) to guarantee low end-to-end (E2E) latency even under congested links. SDLL provides a flexible and on-demand way to change end-to-end paths and queue configurations (ex., add or remove queues). We conducted extensive experimentation by implementing SDLL using Open Network Operating System (ONOS) and Open vSwitch (OVS) tools and comparing its performances against two standard solutions: SDN Shortest Path (SDNSP) (one queue per port) and Software-Defined QoS (SDQoS) (three queues per port). Obtained results indicate that SDLL can guarantee low E2E latency compared to the two other solutions, particularly when: (1) the links are congested and (2) many low-latency critical services are run in parallel.