Thome is expected to be in uniform for tomorrow's game against the Indians.
Executive vice president Dan Duquette told reporters that the two sides were engaged in trade talks for about a week before completing it today.
"Jim Thome's a real pro and he specializes in hitting home runs and getting on base. He's done that consistently his whole career," Duquette said.
"Beyond that, he's a terrific teammate and a steady presence, and he's a veteran. He's been around the league. He's been in the pennant race and he's been in the playoffs. We like all those things that he brings to our team. And I think he gives us a little bit more depth to our lineup with the injuries that we've had. I think his presence in the lineup will make the opposing pitchers work harder because he gets on base and hits home runs and can hit the ball out of any ballpark. We think he'll be an asset to the team.
"With the injury to (Nolan) Reimold, we had to look at adding power to our team. And also, we have a real strong lineup vs. left-handed pitching and I think this will give us a stronger lineup particularly vs. right-handed pitching, So, we were looking to balance our ballclub."
Duquette said there are no concerns about Thome's back.
"He's been hitting and that's his primary asset and he should be able to hit," Duquette said.
The Orioles had to give up Simon, a former fourth-round pick, and Lino, regarded as a catching prospect and someone who's been noticed by manager Buck Showalter and referenced on a few occasions.
"We thought that Thome's presence and our need for the major league team were worth the value that we have to give up in a trade. Both are in A-ball and we needed some help to bolster our lineup," Duquette said.
Thome, 41, is a five-time All-Star and is currently tied with Sammy Sosa for seventh place on the all-time home runs list with 609. He's second among active players behind Alex Rodriguez (642) and trails only Barry Bonds (762) and Ken Griffy Jr. (630) among left-handed batters.
Thome's 1,689 career runs batted in are 25th all-time and his career OPS of .959 is 18th in major league history. Thome is one of eight players in major league history to have 12 or more seasons with 30 or more home runs, joining Hank Aaron, Rodriguez, Bonds, Mike Schmidt, Manny Ramirez and Jimmie Foxx.
In 67 career games at Camden Yards, Thome has hit 18 home runs (one every 13.6 at-bats), scored 45 runs and driven in 45 runs. Thome has hit two balls onto Eutaw Street.
"I really like Thome's makeup and I like that he walks, he takes pitches and he gets on base and he can hit the ball out of the ballpark," Duquette said. "He's a terrific presence and he's proven. He's been around the league and he's a good teammate."
To make room for Thome on the 40-man roster, the Orioles designated Triple-A Norfolk left-handed reliever Zach Phillips for assignment. In his only appearance for the Orioles in 2012, Phillips allowed two earned runs on three hits and two walks in two-thirds on an inning.
As for today's game, the Oriole are losing, 10-5, in the eighth inning. They could use some pitching, too.
Update: Someone has to come off the 25-man roster tomorrow to make room for Thome. The Orioles probably will go back to a four-man bench, and Tommy Hunter could be optioned to Triple-A Norfolk after allowing five runs and eight hits in 1 2/3 innings today. He also walked a batter and struck out two. His ERA is up to 6.11.
Hunter isn't listed among the upcoming starters. He's a prime candidate to be sent down.