The commission said Kenyatta won Tuesday's election with 54 percent of the vote.
Many Kenyans fear a repeat of the violence that followed the 2007 contested election, when about 1,200 people were killed and hundreds of thousands displaced as political protests led to ethnic killings.
Kenyan Sen. James Orengo told reporters: "This has been an entire charade".
Kenya's President Uhuru Kenyatta (L), flanked by his wife Margaret Gakuo Kenyatta (2-L), leaves following a speech after the Electoral Commission's official announcement of the election results on August 11, 2017 at the Bomas of Kenya in Langata, Nairobi. "And I am certain that there is no single Kenyan who would wish for us to go back to this", Kenyatta said.
The 55-year-old Kenyatta will be serving his second and final five-year term in office in line with the requirement of the Constitution.
In the southwestern town of Siaya, a police officer speaking on condition of anonymity said a man had been shot dead in protests, but "we have not managed to collect the body. because of resistance from protesters". As recently as Thursday, Odinga's campaign manager, Musalia Mudavadi, declared victory for his candidate, saying that "a serious attempt to try to either doctor or alter the final results" had fraudulently swung the balance of the election.
Police, who were deployed in anticipation of the results, have fired tear gas in several locations. Additional police have also been installed at the airport in the western city of Kisumu as a preventative measure, according to Reuters.
In Mathare, Wycliff Mokaya said his nine-year-old daughter was killed by a stray bullet while on their third-floor balcony. "She was my only hope".
Worldwide observers, for their part, have lent their blessing to the electoral process in Kenya, saying that despite "minor variances" the election was conducted freely and fairly. "They are not demonstrators but criminals", he said.
He also announced the arrest of people who spread "inflammatory" messages on social media to create insecurities in the country.
In his acceptance speech after being declared the election victor by IEBC Chairman Wafula Chebukati, President Kenyatta called on Odinga, his supporters and MPs elected under his coalition to accept his olive branch and "work to grow Kenya together".
While veteran opposition leader Odinga, 72, claimed 2013 polls were stolen from him, he took his grievances to the courts and ended up accepting his loss.
His opponent Raila Odinga insists the election results have been manipulated, and protests have broken out in poor neighbourhoods in two of the country's major cities.
Police had beefed up security across much of Kenya - particularly in opposition strongholds in the west and parts of Nairobi - in anticipation of the announcing of the election result on Friday.
Odinga has provided documents allegedly showing a database being manipulated, as well as documents purported to be from the IEBC server showing him to be the true victor.