"He's earned it," D-backs manager Kirk Gibson said before a team workout at Chase Field on Thursday. "We thought it was appropriate that he was the next guy to deserve that opportunity."
Allen, a first baseman who has played with the D-backs in parts of the past two seasons, will be called up from Triple-A Reno before Friday's series opener against the Dodgers.
"He's going to get a lot of playing time," Gibson said. "He's played well. He's always had really good production numbers, and we're looking for more production out of that spot."
Allen's addition will accompany the activation of infielder Geoff Blum from the disabled list, while first baseman Juan Miranda will be outrighted to Reno and outfielder Wily Mo Pena designated for assignment.
The 25-year-old Allen hit .306, with 18 home runs and 66 RBIs in Reno this season. In two big league seasons, he has hit .221, with five home runs and 20 RBIs in 149 at-bats.
"I'm just going to be patient, and things will fall my way," Allen said. "When I get up there and get an opportunity, I'm going to take advantage of it."
Allen was drafted in the fifth round by the White Sox in 2004, and traded to the D-backs for reliever Tony Pena in July 2009.
With the D-backs in 2009, he hit .202 with four home runs and 14 RBIs, and last season, in only 45 at-bats, hit .267 with a home run and six RBIs.
"He's got experience here," Gibson said. "He actually wasn't that far away in Spring Training. And when we sent him down, we gave him parameters to work with and what we expected out of him.
"He runs better, he's got power, he's very athletic, and I think he gives us better defense at first base."
Gibson said Miranda took the demotion positively, and will use it as an opportunity to improve.
"This isn't like a goodbye thing," Gibson said. "We still believe he can play more consistently than he has recently.
"It's not easy for anybody. It got to the point where he was playing OK, then it started going the other way on him and he started pressing."
Blum will make his team debut sometime soon, after missing the first 92 games recovering from knee surgery in Spring Training.
He's played both first and third base during his rehab assignment in Reno, where he went 6-for-14 at the plate.
"I'm extremely excited," Blum said. "I've been wanting to play in this city and in this stadium for a couple of years now.
"It will be nice to finally put the uniform on and make it official."
Blum signed as a free agent in the offseason, and has played 12 big league seasons.
The switch-hitter said that he'll play anywhere, and that his swing feels good from the right side -- with his left side not far along.
"If I had to choose, I'd probably choose anywhere on the field," he said about his position. "I'm ready to try and contribute to what's been going on."