He was born to a Hakka Chinese father, U San Pe, and a Burmese mother, Daw Shwe Lai.

Throughout his army career, San Yu rose through the rank quickly due to his steadfast loyalty towards his superiors.

After the 1962 military coup, Brigadier General San Yu became Deputy Chief of Staff of the Army on 15 February 1963.

In the closing day of the Fourth Congress of the BSPP, Ne Win also announced his intention to retire from the position of 'President of the Socialist Republic of the Union of Burma' after the 'elections' in October 1981.

On 9 November 1981 the then Burmese Legislature (Pyithu Hluttaw) elected San Yu as the President of the Socialist Republic of the Union of Burma.

After his retirement, throughout the turmoil that ensued the 1988 pro-democracy demonstrations and military coup, San Yu stayed out of the political societies and lived with his family in his suburban Yangon home.