Dr Lindsay Neil has called for the new road to be one of the key priorities should a bid for Â£1bn worth of "city deal" funding be successful.
He claims a bypass could reduce pollution in the town, especially around the high school.
Transport Scotland said it had invested in "route management" to improve safety on the road.
There has been a lengthy campaign for the A7 to be diverted around the Borders town.
Local people have claimed that the road through the town is unsafe due to the high volume of traffic and large lorries that use the route.
Dr Neil said: "If you are trying to invest money in the Borders, one of the things we have go to do is invest in the infrastructure.
"The A7 is appalling. There are two right angles [bends] in Selkirk. The dangers to the citizens is horrendous. They wouldn't be accepted in the south of England, I can tell you."
A bypass could also benefit the health of vulnerable groups such as the young and the elderly, he added.
He said recent research on pollution levels from diesel cars may add weight to the argument for a ring road.
In a letter to local MSP Paul Wheelhouse, he said: "As a GP practising in the town, I had noticed a marked rise in asthma levels over the years since 1973, when I came, which exactly coincided with the increased use of diesel engines.
"Elsewhere, clear evidence has been accumulated directly blaming diesel emissions as the cause of what is now called the 'asthma epidemic'."
He said children who walk along the A7 to get to Selkirk High School are at particular risk.
Dr Neil has asked Mr Wheelhouse for help in testing roadside pollution levels in the town.
A Transport Scotland spokesman said the bypass was considered as part of its Strategic Transport Projects Review.
He added: "While the review concluded that the Selkirk bypass would not meet the objectives of continuing accident reduction rates across the trunk road network, it did recommend active route management with targeted investments to provide safety and operational improvements, and we have provided more than Â£20m since 2007 to meet those commitments."
A bypass around Selkirk could reduce chronic health conditions such as asthma, according to a retired GP.