Trump Jr. was involved in the selection of Trump's pick for interior secretary, according to a source familiar with the discussions.
He made phone calls to multiple candidates and participated in interviews with the candidates and his father, according to the source.
She also spoke with Argentine President Mauricio Macri when he called to congratulate Trump on his victory.
The transition pushed back forcefully on a report Wednesday that Ivanka Trump will receive office space in the East Wing of the White House.
"This is false," Trump transition spokeswoman Hope Hicks told ABC News. "No decisions regarding Ivanka's involvement have been made."
The Trump transition has defended the Trump family's role in the transition process.
"We've announced that right from the beginning. And so, it only makes sense if a transition team member was active in the process," transition spokesman Jason Miller said on a call with reporters Wednesday morning.
The president-elect also postponed a news conference where he was set to announce plans for separating himself from his businesses interests -- which present an unprecedented potential for conflicts-of-interest when he takes office.
He tweeted that he would leave his businesses to his sons and executives before the inauguration.
"The President-elect has been focused on putting a team in place to enact real change starting on day one," a transition spokesman said in a statement. "With so many iconic properties and successful entities, moving the announcement to January ensures the legal team has ample time to implement the proper protocols so his sole focus will remain on the country and achieving his ambitious agenda with the help of the world-class cabinet he has built."
ABC's Lauren Pearle contributed to this report.