Yesterday, at the age of 47, he relinquished Environment, Climate Change and Local Government.
Out of the gang of four, Mr English rose the highest, to Deputy Prime Minister and Finance Minister.
Roger Sowry, the fourth, and now retired from politics, joined his former colleagues in Dr Smith's office yesterday for the political wake.
Later Mr English paid tribute to his colleague, saying he hoped he would continue to play an energetic role in the caucus around water issues, the Emissions Trading Scheme and local government reform. "The scope of his reach is enormous and he was always on top of those issues. You might disagree with him but you could never accuse him of not doing his homework." He could master very complex issues and communicate them in language anyone can understand "and that's how he held the Nelson seat for such a long time".
New National MPs are often referred to Dr Smith for tutelage in how to be an effective local MP, as he has held his seat often against general trends. Dr Smith's most prized portfolio was Environment which until yesterday he had held since 2008.
Long ago he had picked up where Simon Upton left off in terms of leading the environmental wing of the National Party and he started the Blue-Greens ginger group.
In his first term in the present Government he oversaw amendments to dilute the Emissions Trading Scheme - as promised in the election campaign - and joined Tim Groser in international climate change negotiations. His ACC portfolio was equally as controversial as he sought to discredit its management under the previous Government.
This term Dr Smith was moved down the ranks to the second bench as Mr Key sought to promote more women to his front bench.
Dr Smith is known as an intense person, a politician who gets deeply involved in issues, sometimes too deeply. He was found guilty of contempt of court for revealing details of a family custody case he got involved with in his electorate.
He was also sued for defamation by preservative producer Osmose New Zealand over comments he made about a timber product in 2005. The case was eventually settled out of court in 2010, when Dr Smith apologised and made an undisclosed payment.
Mr English said Dr Smith was someone who focused on finding solutions. "He is a guy who makes decision quickly and sticks to them and he can be hard to shift. Equally he has the same focus on helping people and over the years most of the scrapes he has been in are from being very focused on helping people and pushing it pretty hard."
One of his biggest scrapes occurred in 2003 when Don Brash rolled Mr English as leader.
Dr Smith had been doing the numbers for Mr English and was devastated at the result. As part of Dr Brash's repair job with a divided caucus, he offered Dr Smith the deputy's job.
But the strain surrounding the events became too much and after some erratic behaviour at Parliament, he was ordered to take stress leave.
Gerry Brownlee then replaced him.
The ups and downs of Dr Smith's private life have also made headlines during his time in Parliament. In 2005, he separated from his wife of 20 years, with whom he had two children. He remarried four years later, becoming a stepfather to two more children.
