Grenell, a 50-year-old Michigan native, is a former spokesman for the US at the United Nations and was one of the President's earliest and most vocal foreign policy supporters, vociferously backing the real estate magnate at a time when many in the Republican foreign policy establishment were publicly and staunchly opposed to his candidacy.
An administration official said nothing has been formalized, but last week Grenell posted to Twitter a photo of himself
with Trump inside the Oval Office with the words "Thank you, Mr. President."
The administration official, who spoke on condition of anonymity said Grenell's "very long service at the United Nations and during the Bush administration and the contacts he established through that are very strongly in his favor."
"I think it's natural the President would want to put him in a position he considers important," the official said, adding that nothing has been confirmed. "In the event this comes to be, it seems a very logical appointment."
Grenell, who has worked as a Fox News commentator, would come to the job in Germany with diplomatic experience, a dash of controversy and the personal distinction of being Trump's first openly gay ambassador nominee.
Grenell gained notoriety for snarling attacks on Obama administration officials and a Twitter feed that he used to hurl darts at Democratic women and even Republican targets such as Newt Gingrich and his wife Callista, now nominated to be Trump's ambassador to the Vatican.
While his commentary gained him fans among conservative circles, the fact he's openly gay made some social conservatives uneasy. At the very least, his aggressive tweets and comments were likely a factor in his dismissal from the campaign of then Republican presidential candidate Mitt Romney in 2012.
Grenell was the longest serving US spokesman at the United Nations, serving four ambassadors to the UN under President George W. Bush. During that time he regularly stepped in for the ambassador to represent the US inside the Security Council.
And, at a time of a reported strain in ties between the US and Germany
, where Trump is deeply unpopular, Grenell has long experience working with German counterparts, both on the issue of Iran sanctions and UN reform.
He would have to manage differences between Trump and German Chancellor Angela Merkel on issues ranging from climate change and the Paris Accord to immigration. Trump has broken conventions by publicly criticizing Merkel for her position on the refugee crisis and has repeatedly rapped other NATO members for not spending more on defense and their militaries.
Beyond managing conflicts, Grenell's portfolio would cover the vast array of German-US cooperation that extends from intel sharing and military cooperation to trade. The deal to restrain Iran's nuclear program, which Grennell has called "weak," would likely be a focus of his diplomacy with Berlin as well.
With the Trump administration expected to increase sanctions against Iran outside the nuclear realm, Grennell is expected to flag increased trade with Iran by German companies as a problem.
Grenell also worked for Arizona Sen. John McCain, a Republican, during his unsuccessful 2000 Presidential campaign.
Grenell is a cancer survivor, having been diagnosed with non-Hodgkin's Lymphoma, and went on to found chemoWave, a chemotherapy app for cancer patients.