As per referendum legal sense. It can be deduced that the first Kenyan President Mzee Jomo Kenyatta and his successor Daniel arap Moi, governed without electorates instilled constitution.
Why do I says so, is from Kenya’s constitutional development history I learnt in high school as outline below.
The first constitution in Kenya, was the Lyttelton Constitution of 1954, led by Michael Bludell.
However, in October of the same year the new Colonial Secretary Lennox-Boyd proclaimed the Lennox-Boyd constitution to replace that of Lyttelton.
In January 1960 after the Lancaster Constitutional Conference in London, a another constitution was conceived and new African political parties developed which were subjected to a vote instead of the constitution itself where KANU won in 1960.
A second Lancaster Constitutional Conference was held in February 1962. In order to bring about a compromise between KANU and KADU, a strong Central Government was set up with a federal constitution.
Within the first year of Kenya’s independence, a new constitution made Kenya a Republic. It provided for an executive president and abolished the regional governments.
On December 12th, 1964, the Republican Constitution came into force and prime minister, Jomo Kenyatta, became the first president.
So, I opines that, the former President Mwai Kibaki is the one who gave Kenyans their first voted constitution in November 2005 and the Constitution of Kenya [Amendment] Bill, 2020, also known as Building Bridges Initiative [BBI] is the third amendment of Kenya’s voted constitution from independence.