The economist and policy expert - a former director-general of Saga - will be tasked with making the case for older workers within the business community and challenging outdated perceptions.
The move follows the Government's publication last month of Fuller Working Lives - A Framework For Action, which set out the benefits to individuals, business and the economy as a whole of people aged between 50 and state pension age staying in work.
Dr Ros Altmann said: "I am so pleased that the Government has shown it recognises the importance of encouraging people to stay in the labour market, rather than giving up before they need to.
"This will bring benefits all round - to individuals, to business and to the economy as a whole. A big part of my role is to work with employers to understand the significant benefits of retaining and recruiting older workers.
"I am really proud to be taking on this new role and look forward to championing over 50s in the workplace.
"This fast-growing section of society has so much experience and talent to offer and could play a vital role in future growth."
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She added: "Everyone can benefit from ensuring their skills do not go to waste. I also look forward to challenging some of the outdated and downright inaccurate perceptions of later life workers who still have so much to offer."
Pensions Minister Steve Webb MP said: "In appointing a Business Champion for Older Workers I wanted a powerful voice; someone respected amongst the business community, with a track record of speaking up for consumer rights without fear or favour. In Dr Ros Altmann that's exactly what we have."
Baroness Greengross, chief executive of the International Longevity Centre-UK, said: "Without more older workers active in the workplace there are significant risks for UK plc that we will not have the workforce or skills we need to be a competitive nation.
"Businesses must wake up to the challenge of extending working lives."