Ofcom will address the BBC's "lack of transparency as a matter of urgency" for failing to publish its reasoning for its initial decision over Naga Munchetty, and the Director-General's move to reverse it.
The BBC's executive complaints unit (ECU) last month ruled that BBC Breakfast presenter Munchetty breached editorial guidelines when she remarked on comments made by US president Donald Trump telling female Democrats to "go back" to where they came from.
The ruling was overturned last week by Lord Tony Hall following a large public backlash.
However, Ofcom has said that, following its own assessment, the July 17 broadcast of BBC Breakfast was duly impartial in accordance with the Broadcasting Code, and that an investigation was not justifiable.
The media regulator said it has received 18 complaints, the majority of which related to the fact the ECU initially partially upheld a complaint against Munchetty.
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Kevin Bakhurst, Ofcom's group director for content and media policy, said: "Due impartiality rules are vital for maintaining high levels of trust in broadcast news.
"We took into account the format of the BBC Breakfast programme and the nature of the presenters' exchange. Our assessment is that it would not breach our broadcasting rules and does not warrant investigation."
Mr Bakhurst added: "More widely, we have serious concerns around the transparency of the BBC's complaints process, which must command the confidence of the public.
"We'll be requiring the BBC to be more transparent about its processes and compliance findings as a matter of urgency."
Ofcom said that the exchange between Munchetty and her co-host Dan Walker was not considered to have breached due impartiality rules.
The watchdog has published correspondence between the BBC and itself following what they said was a "lack of transparency" from the broadcaster.
A BBC spokeswoman said: "We note Ofcom's finding and the fact they agree with the Director-General's decision."
Following the complaints, Ofcom assessed the programme and said that "overall, the programme was duly impartial".
The media watchdog said: "After carefully considering all the contextual factors, such as the format of the programme, the nature of the exchange and the specific remarks, we did not consider that Naga Munchetty and Dan Walker's discussion would have breached the due impartiality rules in the Broadcasting Code.
"Therefore, we do not consider that the programme raised issues warranting investigation by Ofcom."
They went to say that they had opted to publish correspondence between the BBC and itself, following what they said was a "lack of transparency" from the BBC.