"I swear to defend the constitution of the United Mexican States and its laws, and faithfully and patriotically carry out the post of president of the republic that the people have entrusted to me," Al Jazeera quoted Lopez Obrador saying before the Congress on Saturday.
The 65-year-old left leader swept the presidential poll with over a whopping 50 per cent votes in July, resulting in a historic first landslide victory after almost 20 years.
Holding the majority in Congress, Obrador would now enjoy the confidence of at least 56 per cent approval ratings, as compared to his predecessor, Enrique Pena Nieto, who would demit office with a mere 28 per cent approval.
Under Nieto's administration, which was engulfed in corruption scandals, crime-related murder rates reached record-high levels in the North American country.
During his campaigns, he had promised to put an end to the violence ensuing in the state under the previous dispensation.
"I understand you can't fight violence with more violence; to put out fire with fire," he had said during the campaign.
One of the major challenges that Obrador is expected to face after assuming office is addressing the ongoing Central American migrant crisis at the border with the United States.
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