Sirianni, 39, had an extensive interview for the head-coaching job that started Tuesday and reportedly spilled over to the next day.
There was a sense in league circles that the race had narrowed to two candidates -- New England Patriots offensive coordinator Josh McDaniels and Sirianni, who has been the Colts' coordinator for three seasons.
Philadelphia ended up hiring the less-heralded name but one that continued to gain steam inside the Eagles organization the more it called around about him.
The Eagles' coaching search was done with the quarterback situation -- Carson Wentz, in particular -- in mind. After firing Doug Pederson, whose relationship with Wentz had soured, Eagles owner Jeffrey Lurie said: "It behooves us as a team with a new coach, a new coaching staff, to be able to really get [Wentz] back to that elite progression."
Wentz, whose struggles in 2020 were described as "very fixable" by Lurie, was benched for the final quarter of the season after consistently poor play. Rookie Jalen Hurts replaced him in the lineup and provided a spark to the offense but cooled some down the stretch.
Wentz had a near-MVP campaign in 2017 when current Colts coach Frank Reich was his offensive coordinator in Philadelphia.
Sirianni was Reich's right-hand man in Indianapolis and was the quarterbacks coach when Reich was the Chargers offensive coordinator in 2014 and '15. The connection could hold significance for Wentz, who has a great deal of trust in Reich.
Wentz had been expected to request a trade this offseason because his relationship with Pederson was fractured beyond repair, according to ESPN's Chris Mortensen.
Both Hurts and Wentz are under contract with the Eagles for 2021.
Despite a rotating cast at quarterback with Andrew Luck, Jacoby Brissett and Philip Rivers, Indianapolis fielded a top-10 offense in two of the past three seasons. Rivers completed 68% of his passes this season for 4,169 yards with 24 touchdowns to 11 interceptions in 2020.
The Colts (11-5) finished ninth in the NFL in scoring (28.2 PPG) and 10th in yards per game (378.1) in 2020.
Sirianni has worked as a quarterbacks coach and receivers coach since coming into the league with the Kansas City Chiefs in 2009.
The Eagles held an extensive search after firing Super Bowl-winning coach Doug Pederson on Jan. 11. They interviewed Arthur Smith, Robert Saleh, Jerod Mayo, Joe Brady, Kellen Moore, Duce Staley, Todd Bowles, Dennis Allen, McDaniels and Sirianni. They also had a request in to speak with Buffalo Bills offensive coordinator Brian Daboll, sources said, but there was an agreement to wait until after Sunday's AFC Championship Game for a potential interview.
Pederson was fired after going 4-11-1 in his fifth season with the team. He went 46-39-1 and won the Lombardi trophy during the 2017 season -- the first of three straight playoff appearances for the Eagles under Pederson.