A progressively curved lumbar support located within the back of an office or home chair to enable a user to be seated close to a work surface (e.g., a desk or a table). The chair back tilts backwards and forwards when the user shifts his weight back and forth. The lumbar support includes a cushion back support manufactured from a resilient material that is responsive to a compressive force applied thereto when the user reclines against the chair back. In particular, a tilt pressure-responsive rod rides up and down over a pair of inclined guide blocks to cause the cushion back support to change its shape from a convex configuration at which to support the user's lower back and maintain a proper posture when the user sits erect and the chair back stands upright to a relatively flattened configuration when the chair back tilts backwards.