Police spokesman Enrique Torres said the Mexican army arrested the suspect, whose name was not released, on Friday.
Consulate employee Lesley A. Enriquez and her husband, Arthur H. Redelfs, were killed March 13 in Juarez when. Their 7-month-old daughter was found wailing in the back of the vehicle.
Jorge Alberto Salcido, the husband of a Mexican employee of the consulate, also was killed by gunmen after leaving the same event in a separate vehicle.
Torres said the suspect is a leader of the Barrio Azteca gang, but gave no other details. He said the suspect would be presented to the media later Monday.
U.S. and Mexican authorities say the Barrio Azteca gang works for the Juarez drug cartel and operates on both sides of the border.
Initially a Texas prison gang, Barrio Azteca expanded across the Rio Grande into Juarez in the late 1990s, U.S. authorities have said.
Last week, El Paso police and Texas state troopers arrested 25 people in a sweep of suspected gang members.
Ciudad Juarez, across from El Paso, Texas, is one of the world's deadliest places. More than 2,600 people were killed last year, and another 500 so far this year in the city of 1.3 million.