Both leased lines and MPLS provide WAN (Wide Area Network) connectivity. MPLS usually functions by being implemented as a full mesh, while a leased line functions by establishing a connection between two points. Actually, the full meaning of MPLS is Multiprotocol Label Switching.
It is known as a mechanism that carries data. In the MPLS network, you assign labels to data packets. MPLS permits the creation of end-to-end circuits by using any protocol across all transport medium types. The MPLS framework is a bit complex. It also depends on some data link technology like frame relay, synchronous optical networking.
A leased-line is referred to as a service contract between a provider and a customer. A consumer pays the provider most likely on a monthly basis after the provider must have provided asymmetric communication line that connects several locations. There is no telephone number involved, and lines are connected to themselves.