The frontman has signed a three-year deal with the Millers just days after leaving fellow Championship side Nottingham Forest and delighted manager Alan Stubbs has pledged to have the 30-year-old ready for action without delay.
“In terms of his fitness, he has been training regularly, but hasn’t necessarily got the required game-time that he has been looking for,” Stubbs said.
“We will be looking to get that into him as quickly as possible and get him on the pitch doing what he does best.”
Blackstock - who made his debut in 2004, in the Premier League as a youngster with Southampton against an Everton side that included Stubbs at centre-half - became a free agent after leaving the City Ground by mutual consent last week.
The Antigua and Barbuda international is a proven performer in the second tier and was a Millers target during the transfer window which closed six days ago.
Stubbs had been searching for a centre-forward all summer, and there may be a second free-agent arrival on the horizon as chairman Tony Stewart told The Star last week that Rotherham were in the market for more than one striker.
Stubbs added: “I am delighted. This is one that we were trying to conclude before the deadline but, due to negotiations that Dexter was having with his club at the time, there wasn’t enough time.
“I think this is a deal that we have had to be patient with. Our persistence has now paid off because we have managed to get the right player.
“He brings a wealth of experience in The Championship. He will give us an added dimension in terms of how we can play as a team. I am really happy now that we have managed to get the deal over the line.”
Blackstock rose to prominence at Queens Park Rangers by scoring 30 goals in 109 league appearances, earning himself a £1.5 million move to Forest in 2009.
The six-footer bagged 43 goals in 170 league games for Forest. He came off the bench during Forest’s 2-1 home win over Rotherham in August 2015 last season and was a thorn in the Millers’ side in the 0-0 draw at New York Stadium in April this year.
He was born in Oxford but is an Antigua and Barbuda international. After playing for England Under-21s earlier in his career, he made his Antigua and Barbuda debut in 2012 and scored later that year against the USA in a World Cup 2014 qualifier 2-1 defeat. He has made six international appearances, scoring twice
During his time with Southampton he went in goal for the final 10 minutes of a 2006 FA Cup fifth-round tie against Newcastle when Saints goalkeeper Bartosz Bialkowski was injured and all three substitutes had been used. He didn’t concede but the Saints were already behind and lost 1-0.
In the opening game of a loan spell with Leeds United in 2013 he scored with his first touch after coming on a sub in the West Yorkshire debut against Huddersfield Town. His goal made the score 2-2, but Huddersfield ran out 3-2 winners. The scorer of the opening Terriers goal that day was a certain Danny Ward, now a teammate of Blackstock at New York.
Blackstock follows a well-trodden path from the City Ground to New York, with Matt Derbyshire, Greg Halford, Danny Collins, Chris Burke and Kelvin Wilson making the same journey in recent seasons.