HS2 should be built in its "entirety", according to the director of Midland Connect, a body that lobbies for improvements in transport on behalf of Midlands councils and businesses.
Maria Machancoses told BBC Radio 4's Today programme that the benefits of the high-speed rail link had been "hugely under-estimated" by critics who want to see the project scrapped.
She said Birmingham had seen a "huge transformation on the back of the announcement that HS2 is coming to the city".
"HS2 needs to be delivered in its entirety," said the transport expert.
"HS2 is not just about connecting the Midlands to London.
"It is about connecting the Midlands to the North and it will, actually - most importantly - deliver the released capacity we so desperately need in our local railway networks. It is a national priority, it has to be delivered."
It comes after Lord Tony Berkeley, HS2 critic and Former Deputy Chairman of the review into the high-speed route, said local improvements should be prioritised above HS2.
The Labour peer has released a report saying MPs were "misled" over the £55 billion infrastructure price tag, and claiming that costs are set to rise to almost double that figure.
Speaking to the BBC, Lord Berkeley said: "All the benefits we have heard about I believe could be achieved by a massive improvement to the existing lines in the travel-to-work areas around Birmingham and Stafford.
"The problem is, if you spend £107 billion on HS2, you probably need to spend another £50 billion to improve all the commuter lines into and around Birmingham so that you can get the full economic benefit.
"Nobody has told me whether the attraction of business that we have heard about is caused by HS2 or could equally well be caused by an improvement to the existing lines - to electrify them and make trains more frequent, things like that."
Conservative MP for Brigg and Goole Andrew Percy urged the Prime Minister to make a decision on the route quickly, as the much-awaited Oakervee Review was due.
“As soon as possible, we need to get certainty on HS2 and HS3 Northern Powerhouse Rail,” he said.
“I don’t want it to be one or the other, we need to have both across the North.
“We’ve been talking about it for so long, it would be nice to have some certainty on when it’s going to happen.
“We’ve had so much talk about connectivity in the north from governments of both colours for many years," he told The Daily Telegraph.
But the Prime Minister's Official Spokesman today said no date had yet been set to release the review.