The election board said on Saturday that Abiy's Prosperity Party won 410 out of 436 seats, giving him another five-year term in office.
However, a fifth of the country failed to carry out voting overall due to insecurity and logistical problems.
Polls were not held in the war-torn Tigray region, where hundreds of thousands face extensive famine.
Another round of elections has been penned for September 6 in the affected areas, but a date has not been confirmed for Tigray, following the delay of polls due to the pandemic, but rebel leaders in Tigray proceeded with their own polls and won the local mandate for the Tigray People’s Liberation Front (TPLF).
Abiy, winner of the Nobel Peace Prize for his reforms and reaching peace with Eritrea, described the vote as a "historically inclusive election" in a statement on his twitter page.
A new government is expected to be formed in October. However, there are concerns about the election's integrity, with opposition parties complaining that a government crackdown against critics had disrupted their polls preparation plans.
Aby critic Berhanu Nega said his party, Ethiopian Citizens for Social Justice, had filed more than 200 complaints after observers in a number of regions were blocked by local officials and militiamen.
The state-affiliated Ethiopian Human Rights Commission (EHRC) said there were "no serious or widespread human rights violations" in stations it observed.
However, in a preliminary report the EHRC said that some constituencies experienced improper arrests, as they recorded voter intimidation and harassment of observers and journalists, noting also that it had observed several killings in the days leading up to the vote in the regional state of Oromia.
In May, the EU accused Ethiopia of failing to guarantee the independence of its election.
The election was Mr Abiy's first electoral test since coming to power in 2018.
He has clamped down on corruption, released political prisoners, appointed more women to the cabinet and made peace with neighbouring Eritrea, following a 1998-2000 border war that left tens of thousands of people dead.
He won the 2019 Nobel Peace Prize, but just a year later, he launched the military operation against Tigray province to oust the TPLF as the party defied the federal authorities, seizing military bases in the region in a move that observers interpreted differently, either as bid to overthrow Abiy, intention of secession or forceful demand for a weaker federal structure.
The conflict in Tigray has killed thousands of people more from food insecurity than military operations, as many abandoned their towns and villages to seek shelter across the border in Sudan. Eritrea forces, traditional enemies of TPLF, carried out operations laced with brutality, external observers maintained.
On Saturday, for the first time in two weeks, the UN World Food Programme began moving aid into Tigray, following weeks of trading accusations on blocking much-needed shipments.
The UN said on Friday that humanitarian operations were being constrained by the absence of essential services including fuel, telecommunications and electricity.