While HMD did not state the reason for the sudden departure, it said "through mutual agreement between Chief Executive Officer Arto Nummela and the HMD Global Board of Directors, Arto Nummela will leave HMD with immediate effect".
Florian Seiche, who is currently serving as President, will take over the additional responsibility as acting CEO, the Finnish firm said in a statement.
Seiche had been co-leading HMD Global as President since the start of the company.
HMD had acquired the manufacturing and distribution assets of the former Nokia phone business from Microsoft last year.
Earlier this year, HMD revived Nokia's classic 3310 feature phone and is looking at bringing in more such devices as it aims to tap into growth markets like India and countries in Africa.
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