Convertible motor vehicle seat

The seat has a support constituted of two frames (6) whose sides are formed of rigid units (8-11, 8-11) articulated with each other by articulations (A12-A15) placed at each of their ends on respective axes (12-15) such that the support can be deformed quadrilaterally. A base (2) is articulated on an axis (14). A backrest (3) is mounted on an end of an arm (16) placed at both sides of the seat by a lockable articulation (A19). Independent claims are also included for the following: (A) a vehicle comprising a seat (B) a method of transforming a transformable seat.