The California-born striker was part of the Stars and Stripes team that won back-to-back World Cups in 2015 and 2019, prior to which she had also become the first player to score and assist in a World Cup final in the USA's 2011 loss to Japan.
Before her World Cup triumphs, Morgan became and Olympic gold medallist with the USA at the London 2012 Games, but she was left out of Emma Hayes's squad for the Paris 2024 edition.
Following her Olympics snub, Morgan - who currently plays for San Diego Wave in the National Women's Soccer League - confirmed in a social media video that she had hung up her international boots, 14 years after her USA debut.
As well as admitting that international retirement had been a "long time coming", the 35-year-old also revealed that she was unexpectedly pregnant with her second child, news that left her and her family "so overjoyed".
"I'm going to get to the point quickly: I'm retiring. I have so much clarity about this decision and I'm so happy to be able to finally tell you," Morgan said in a video posted on X.
Morgan to play final professional match on September 8
"It has been a long time coming and this decision was not easy, but at the beginning of 2024, I felt in my heart and soul that this was the last season. Soccer has been a part of me for 30 years and it was one of the first things that I ever loved. I gave everything to this sport and what I got in return was more than I could have ever dreamed of.
"This is also not the retirement video I expected when I initially thought I was going to this, because Charlie is going to be a big sister. I am pregnant. And, as unexpected as this came, we are so overjoyed. To me, family means everything."
Morgan's final match as a professional player comes on Sunday, when the San Diego Wave host the North Carolina Courage in the NWSL, and she retires after scoring 123 goals in 224 matches for the USA.
Only four American women have scored more goals internationally than Morgan, who also sits ninth on the USA Women's all-time appearances list and fourth in the NWSL goals charts with 60 strikes.
At club level, Morgan's crowning achievement was winning the Women's Champions League with Lyon in the 2016-17 season, helping the French giants complete a league, cup and European treble.
The striker also spent a few months with Tottenham Hotspur at the end of 2020, scoring two goals for the North London club, and she was named in the FIFA FIFPRO Women's World 11 six times, level with Lucy Bronze and second only to Wendie Renard's seven.