An after-treatment (AT) system for an exhaust gas flow from an internal combustion engine includes an AT device and an exhaust passage carrying the exhaust gas flow from the engine to the AT device. The system also includes a heat exchanger in fluid communication with the exhaust passage upstream of the AT device and configured to remove heat energy from the exhaust gas flow. The system additionally includes an exhaust gas flow bypass in fluid communication with the exhaust passage and configured to route the exhaust gas flow from the exhaust passage to the AT device around, i.e., in bypass of, the heat exchanger. Furthermore, the system includes a bypass valve configured to selectively direct the exhaust gas flow to one of the heat exchanger and the exhaust gas flow bypass. A vehicle employing the AT system and a method of operating such an AT system are also disclosed.