Bernardo Arévalo, a progressive anti-corruption campaigner from the Movimiento Semilla (Seed Movement) party, secured a decisive win, leading over former first lady and seasoned centre-right politician Sandra Torres with a margin of 58.3 per cent to 36.9 per cent.
These percentages were revealed as nearly all the votes were meticulously counted by the Supreme Electoral Authority (TSE) on Sunday evening.
Arévalo's campaign was centred around combatting corruption and addressing the erosion of democracy in Central America's most populous nation. His ascent to power would signify a transition from the conservative leadership of incumbent Alejandro Giammattei.
Giammattei, who has reached his term limits, was not eligible to contest again, prompting the need for this election.
The voting process saw approximately 9.4 million eligible voters participate in choosing the successor to Giammattei.
The final tally according to TSE figures reflected 4.2 million valid votes cast.
Throughout the election process, concerns arose as the political elite and the Attorney General's office sought legal means to hinder the rise of 64-year-old Arévalo.
The European Union voiced its unease over these developments.
The initial round of voting that took place on June 25 was marked by the disqualification of several prominent candidates, sparking outcry and allegations that electoral officials were manipulating their authority to sway the election's outcome.
Arévalo's remarkable emergence as the second-strongest candidate in the initial round of elections was unexpected.
Taking the top spot was three-time presidential contender Sandra Torres, who, in the previous two elections, fell short in the run-off vote.
A sociologist and former diplomat, Bernardo Arévalo is also the son of Guatemala's first democratically elected president, Juan José Arévalo (1945-1951).
Sandra Torres was married to the late Álvaro Colom, who served as Guatemala's president from 2008 to 2012.
While Torres co-founded the centre-left party UNE, which is the largest political party in Guatemala, she has more recently moved towards the centre-right spectrum, illustrating the fluidity of political alignments. (dpa/NAN)