Though Castro is often billed as a rising star in the Democratic Party, it's debatable whether he even has the best political job in his family.
Castro's twin brother, Joaquin, is a freshman congressman, representing the western half of San Antonio.
Let's take a look at the 39-year-old brothers to see who has the more enviable position in Washington.
Julian, who splashed onto the national stage with his Democratic National Convention keynote speech in 2012, is obviously the buzzier of the two.
His name has been floated as a possible 2016 vice presidential candidate, and he's been dubbed the “Hispanic Barack Obama.”
Before Obama announced the nomination Friday, White House press secretary Jay Carney was asked whether he thought Julian was merely using the housing post as a “stepping stone” to another national job. The president's top spokesman sidestepped the debate, but it certainly will become a popular topic of conversation in Washington.
Such talk could be premature, especially if the recent top office holders at HUD are any indication.
Here's a list of Julian's predecessors (assuming he's confirmed) and the highest-profile jobs they took after leaving the housing agency:
Shaun Donovan is taking over as director of the Office of Management and Budget (assuming he's confirmed).
Steve Preston became president and CEO of Oakleaf Waste Management.
Alphonso Jackson went on to teach as a distinguished professor and director of the Center for Public Policy and Leadership at Hampton University.
Mel Martinez won a Senate seat in Florida.
Andrew Cuomo is now the governor of New York.
Henry Cisneros, also a former mayor of San Antonio, served as president and chief operating officer of Univision Communications.
While HUD could certainly serve as a launching pad for Julian — as it did with with Cuomo — it's far from guaranteed to land him on a presidential ticket.
And Obama's Cabinet members in particular have grumbled about being marginalized in their positions. Donovan, for example, has kept a low profile during his entire stint at HUD.
And some questioned whether HUD would broaden Castro's policy portfolio in advance of a possible vice presidential bid.
“HUD offers Castro no experience in areas where he lacks credentials: national security, defense, international relations,” wrote Texas Republican consultant Matt Mackowiak. “Is HUD really a qualification for the vice presidency?"
Many assume that Joaquin wants to pursue statewide office in Texas, perhaps the governorship or a Senate seat.
“Democrats have to put up somebody strong in 2018 in that Senate race,” Rep. Joaquin Castro told the New York Times, “whether it will be me or not.”
Joaquin's ambitions are seen as more modest than Julian's, but they may ultimately prove more realistic.
“He's also a very talented guy, he's not been quite as ambitious as his brother in getting his name out there,” Texas-based Democratic strategist Keir Murray said. “But most people think by 2018, 2020, Texas will be more competitive politically,” Murray added. “ And, like his brother, he has youth on his side.”
Of all the possible job perks, the paycheck is the most obvious starting point.
If confirmed, Julian would bank nearly $200,000 annually as a member of Obama's Cabinet. In comparison, Joaquin earns $174,000 a year as a new member of the House.
But obviously neither brother is taking the job for the money.
Julian reportedly made more than $200,000 in 2013, most of which came from a book advance. The San Antonio mayor also received five-figure payments as speaking fees (his official salary was just $4,000 a year).
However, some have noted that Julian could come under fire for a seven-figure referral fee he collected as a lawyer in connection with a case involving a drunken driving accident that killed three people. Essentially, Castro passed the case along to a bigger firm and was rewarded with a massive payday, which is still drawing scrutiny.
Julian will soon serve at the pleasure of the president. His agenda is basically the same as Obama's when it comes to housing.
Though Joaquin is somewhat beholden to party leadership, he has more freedom to pursue issues of his choosing.
Still, Julian will get more frequent flier miles, traveling the country to promote the president's housing policies — and perhaps building his brand in the process.
Julian is looking at two and a half more years on the job, unless his tenure is interrupted so he can join a presidential ticket. Really, that's up to possible Democratic frontrunner Hillary Clinton.
And Obama's Cabinet appointees, as demonstrated by Health and Human Services Secretary Kathleen Sebelius and Veterans Affairs Secretary Eric Shinseki, have developed a habit of attracting controversy.
Regardless, the job comes with an expiration date — one that Julian likely doesn't mind all that much.
In comparison, Joaquin won his House seat in 2012 by nearly 30 percentage points. The heavily Hispanic district is a safe Democratic seat, even in red Texas, meaning the job is Joaquin's as long as he wants it and doesn't do anything stupid.
This one isn't even close.
It was Julian, after all, standing next to Obama at the White House on Friday.
And though these jobs are supposedly about “serving the American people,” ego can never be ignored.
Obama, in fact, likened Julian's political rise to his own.
“They saw this young guy, pretty good speaker, not bad looking,” Obama said of Julian's keynote speech in Charlotte, N.C.
“I looked and I thought,” Obama remembered, " 'that's not bad.' ”
Julian has the upper hand on his brother. But his likely confirmation to HUD in no way guarantees him a permanent spot in the big leagues — and Joaquin's aspirations might be a bit more realistic.