"So happy to be in the best team in the nba!!!dallas!!!" Fernandez tweeted.
The deal was arranged before the Mavericks were on the clock with their first selection at No. 26, sources had confirmed to ESPN.com senior NBA writer Marc Stein.
Fernandez has spent his three NBA seasons in Portland. Only 26, he's also been a standout in international play. He could step in as Dallas' starting shooting guard or become another piece in a deep, versatile rotation.
"We're in a playoff-championship push mode," said Donnie Nelson, the Mavericks' president of basketball operations. "We think the player we acquired is going to help us more than the pick would."
Dallas spent the 26th pick on Jordan Hamilton and the 57th pick on Targuy Ngombo. Hamilton went to Denver and Ngombo to Portland in a deal that also involved a swap of Trail Blazers point guard Andre Miller for the Nuggets' Raymond Felton.
The Mavericks also picked up the rights to Petteri Koponen, who is playing in Europe. A point guard from Finland, he's spent three years with Virtus Bologna in Italy.
"Rudy is an athletic, young, exciting player with significant upside," Nelson said in a statement. "His international and postseason experience will prove to be very valuable. Petteri is a young combo guard who was a first-round selection in 2007 and is developing nicely in Europe."
Fernandez has been a backup most of his NBA career. He's averaged 9.1 points over 24.1 minutes in 218 games.
His role in Dallas remains to be determined, but his age and experience make for a nice fit -- especially compared to an unpolished product.
"The balance is a player that's a young one vs. one that's been in the league a few years and can help us right away," Nelson said.
Nelson said this deal had been discussed for a while, heating up in the last few days.
"This was our 'A' scenario," he said.
Shooting guard was an erratic spot for Dallas this past season.
DeShawn Stevenson drew most of the starts in the regular season, then gave way to Rodrigue Beaubois, whom the team was expecting to have a breakout year. But he had trouble recovering from a broken foot and missed time, and Stevenson regained the job in the finale. He started every postseason game until Game 4 of the NBA finals, when backup point guard J.J. Barea took over.
Stevenson is a free agent. So is Peja Stojakovic, another role player whose best skills could be replaced by Fernandez.
Beaubois will be back next season and may get another chance to start. Fernandez could push him for the job or be part of Dallas' bench. Jason Terry already is their primary shooting guard.
This past season, Fernandez averaged 8.6 points in the regular season but scored only 2.8 per game in a first-round series against the Mavericks. He made only 4 of 18 shots.
Mavericks star Dirk Nowitzki likes the addition of Fernandez.
"I think he fits in well," Nowitzki said Friday night after throwing out the first pitch at a Texas Rangers game. "He had a tough time there in Portland sometimes coming off the bench. He wanted out and I don't think the whole situation for him was that great. But when you come to a team that has great team chemistry and good leaders and veterans, guys always fit in well and they want to win and sacrifice and in this case, I think it's going to be great for the team."
Information from ESPN.com's Marc Stein, ESPNDallas.com's Tim MacMahon and Richard Durrett and The Associated Press was used in this report.