The academy graduate initially took his chance in the Villa first team at the start of 2021-22, scoring four times against Barrow and Chelsea in the EFL Cup.
However, they would prove to be his only senior goals for his boyhood club, instead being sent out on loan on numerous occasions.
A situation arose last summer where Sheffield United signed Archer for £15m under the premise that he would return to Villa for a similar fee if they suffered relegation.
That agreement was put in place to help both clubs with the financial rulings, yet it has left the England Under-21 international awaiting a resolution to his future all summer.
Archer was provided with plenty of minutes across pre-season, even featuring against Borussia Dortmund in last weekend's friendly, but he will now make the switch to St Mary's.
How much have Southampton paid?
Although the official word is that a fee will remain undisclosed, transfer expert Fabrizio Romano says that Southampton are paying £15m for the 22-year-old.
Having penned a four-year contract, Archer said: "I'm really excited to be here. I had a good chat with the gaffer. Obviously, he told me everything I needed to hear.
"That was one of the main reasons why I'm here, his playing style, his coaching and trying to improve me as a player. It's not a bad place to do that in the Premier League with Southampton.
"I just want to keep scoring goals and improve myself as a player, and I don't think there's a better place to do that than with Southampton."
Archer will now compete with Adam Armstrong, Ben Brereton Diaz and Ross Stewart for a place in Russell Martin's forward line.
Will Archer become first choice?
At Championship level, Archer has chipped in with 18 goals and seven assists from 40 appearances, but it has been a different story in the Premier League.
Just four goals and one assist came from 29 outings for Sheffield United during 2023-24, a return that he will want to better with his new team.
Archer will not be involved when Southampton face Newcastle United at St James' Park on Saturday afternoon.