The Blues parted company with Kenny Jackett yesterday in a bid to salvage their League One promotion hopes.
Saturday’s defeat to Salford City in the Papa John’s Trophy final proved Jackett’s final game in charge, bringing an end to his near four-year reign.
Chief executive Mark Catlin has now started the recruitment process to find the 59-year-old’s successor.
He guided Millwall to the second tier in 2017, while he also led Cardiff to the Championship play-offs last season.
However, Harris was relieved of his duties in south Wales in January after six straight defeats which left the Bluebirds well out of the promotion race.
Mick McCarthy has since led Cardiff to eighth spot.
Speaking on Sky Sports earlier this month, Harris enjoyed his time at the Bluebirds.
But with Cardiff aspiring for a Premier League return, the 43-year-old admitted results were not good enough.
He said: ‘The demand of the football club, they have been in the Premier League a couple of times in the last seven years, so the expectation of the fan base is to be there again.
‘The expectation of the board was to be a top-six side as often as possible throughout the season and in some ways rightly so, it is a big club.
‘I wouldn't say it was unrealistic, challenging at times during a Covid-hit season, the short turnaround, I think we probably really underestimated the play-off defeat and the mentality for the players and the group with that really quick turnaround.
‘The players literally had five or seven days off between the two seasons, it's tough to come back from that.
‘‘I loved it, obviously. It was a great experience being there, working at a fantastic football club.
‘It is interesting to see Mick's quotes over the last 24 hours, when he signed a new deal, about what a good club it is. It is a really good club, a really good owner, who has really backed the football club over a period of time.
‘It's a huge club. It's not until you're really there, in the heart of it, living in it, in the bay area down there, the amount of fans that are in the area and what they think of the football club and their expectations.
‘I really enjoyed it. First season in charge, came in and went on a similar run to what they are on at the moment, going from lower-mid table to the play-offs last year.
‘Obviously, this year there were different challenges and we didn't get the results we probably needed.’
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