But what did business make of McDonnell's appearance? Here are the reactions:
CBI: "Strong on intent but not on detail"
The shadow chancellor was strong on intent but has not yet provided great detail on how he intends to deliver his plans. The overall impression of this speech was of rather more intervention in the world of business and the economy.What’s clear to us is that you can’t be pro-growth and pro-jobs without being pro-business. And a thriving private sector is essential for raising living standards and paying for high-quality public services.We share the aim of seeing more people getting into higher-paid jobs but pay rises need to be sustainable and affordable - and based on rising productivity. Mr McDonnell talks of working in partnership with businesses and entrepreneurs, and recognises the importance of deficit reduction, infrastructure, and skills. But this is best achieved by liberating entrepreneurs to create wealth and jobs.
BCC: "Don't prejudge outcome of reviews on Treasury and Bank"
There is a difference between an entrepreneurial state - one that supports growth and innovation - and a big state, reaching into and directing every facet of business and national life.... McDonnell is right to go back to first principles and review the shape of the UK economy. He is right to start fundamental reviews of how the Treasury and the Bank of England work. He is right to engage economic experts to look in detail at how the state can better support economic growth.However, he must not prejudge these reviews - or insist on attacking businesses and wealth creators, when a conversation is what is needed. Labour needs to get the tone right if it wants to build a partnership with business, in the national interest.
Louise Cooper: "Economically and fiscally naive"
It's cloud cuckoo land. The job of a chancellor is to live in the real economic and fiscal world. McDonnell does not. A significantly higher minimum wage is likely to reduce demand for labour. More wages, less jobs, classic supply and demand. It is private business that creates long term economic growth and not the government. It only has money to spend thanks to private business. Extravagant promises on spending but with fiscal responsibility? History suggests this is unachievable.
ICAEW: "A new era of politics"
Fixing our public finances is dependent on generating sufficient tax receipts, so we are pleased that our calls for more resource for HMRC to concentrate on tax avoidance have been heard. Reviewing the Bank of England's mandate is perfectly reasonable after 18 years, as is looking at the Treasury. We have suggested that Treasury must be transformed into a modern finance ministry, with responsibility across all parts of Whitehall.We are in a new era of politics, and the Shadow Chancellor spoke of the need for debate. It will be interesting to see what policies Labour come up with in the months and years ahead. Businesses across the country will welcome the opportunity for debate going forward.