The appointment of the three-time major champion, 47, was announced in a news conference at Wentworth on Tuesday.
"I can only look at his actions", said Harrington, who succeeds Thomas Bjorn as captain. He played in three USA Ryder Cup teams and on five winning Presidents Cup sides while he captained the USA Team to victory in the 2017 Presidents Cup.
"We finished on 18 and I thought I'd closed the match out, and that I had won The Ryder Cup", Harrington told the European Tour's Life On Tour Podcast, presented by Hilton.
"The back-room team was flawless and I thought the vice-captains had a great mix", he said.
"But's it's a new venue at an away match and, on average, we are likely to see three more rookies on the team and I want to make sure I help them find and edge and hopefully get a win".
"Then it really came down to whether I wanted to be in the hat and put what is a successful career on the line".
'It's possibly easier to be Ryder Cup captain at home, but I realise it was good timing in my career and probably the best chance for the team in an global setting, going to the United States having me as captain at this time.
The 2020 Ryder Cup will be played from September 25 through September 27 at Whistling Straits in Wisconsin.
"I'm excited with the whole idea, I hope I can add something to it", added Harrington.
Word in the media tent was that Thomas Bjorn had made obvious a desire for his vice-captains to steer clear of casual interaction with anyone outside Europe's team room.
The PGA of America might be tempted to go for someone with a winning pedigree as Ryder Cup captain, with Davis Love III and Paul Azinger top of a very short list!
The desire to intellectualise, even mythologise the role of a Ryder Cup captain has reached such farcical levels of late, you might believe it demands the esoteric judgement of a nuclear physicist.
Harrington is the third Irish golfer to hold the role since 2014.
"I have reached the stage in my career where I enjoy playing golf", Harrington said.
Harrington did slip momentarily towards the modern Ryder Cup taste for melodrama yesterday with an observation that he'd be putting his "career on the line" in Wisconsin.
"I think Steve will be a nice Ryder Cup captain".
"But it is daunting because you want to do a good job".
"I think the standard of golf on the European Tour and the players we have on tour is going to ensure that". He's tough but very straight.