The former head of Mexico's state oil company was arrested on Wednesday in Spain on an international warrant.
Emilio Lozoya was arrested in the southern port city of Malaga.
Mr Lozoya was director of Pemex between 2012 and 2016, during the administration of former President Enrique Peña Nieto.
Mexico issued international arrest warrants for Mr Lozoya last year as a result of corruption investigations, including into his alleged ties to Odebrecht, the Brazilian construction company that allegedly secured contracts across Latin America through a network of bribes.
Officials are also investigating Pemex's purchase of a fertiliser plant in 2015 at an allegedly inflated price.
Mr Lozoya has repeatedly denied wrongdoing.
Gerardo Rodríguez, a political scientist at the University of the Americas in Puebla, called the arrest the “most important blow in the fight against corruption in Mexico".
“Lozoya is the archetype of the corrupt Mexican international technocrat,” Mr Rodríguez said, saying he was close to a former president and involved family members in his business.
Mr Lozoya's mother is currently under house arrest with an investigation open against her.
Observers said it was a win for President Andrés Manuel López Obrador's government and his promises to root out corruption.
“It is a positive sign,” said Eduardo Bohórquez, director of the non-governmental group Mexican Transparency.
He added that “this would have to be the first of many arrests. it remains to be seen whether there is truly a dismantled network and whether the stolen money will be recovered.”
The international manhunt for Mr Lozoya began in last May via Interpol. Spanish authorities had information about him being present in various parts of the country, but his wealth and “international ties made locating him difficult,” Spain's Interior Ministry said in a statement.
He is expected to appear before a judge on Thursday in Madrid.
In late 2016, Odebrecht, reached an agreement with American, Brazilian and Swiss justice officials to pay millions of dollars in penalties.
As part of that accord, Odebrecht divulged details of bribes across several countries. It said it paid $10.5 million to officials at Pemex between 2010 and 2014. Mr Lozoya has denied taking bribes.
