TRENTON -- Phil Murphy, the Democratic nominee for New Jersey governor, will announce he has chosen former state Assembly Speaker Sheila Oliver to join his ticket as candidate for lieutenant governor, a source with knowledge of the selection process told NJ Advance Media.

Murphy, a retired Wall Street executive and former U.S. ambassador to Germany under President Barack Obama, is expected to formally announce the pick as early as Wednesday, according to the source, who is not authorized to publicly discuss the choice and requested anonymity.

The move was not a big surprise. Oliver (D-Essex) -- who is still a member Assembly, though no longer its leader -- has long been considered a front-runner.

In selecting Oliver, Murphy has chosen a running mate who is different from him in just about every way when it comes to identity, upbringing and local politics.

The first African-American woman Assembly speaker in state history, Oliver has more than a dozen years of legislative experience, serving in the lower house of the New Jersey Legislature since 2004.

She also served on the Essex County board of chosen freeholders from 1996 to 1999.

Murphy, who spent 23 years as a banking executive at Goldman Sachs, has never held elective office.

The two have have vastly different educational and professional backgrounds.

Born and raised in Newark, Oliver, 65, graduated from Weequahic High School before moving to Pennsylvania to earn a degree in sociology at Lincoln University, the nation's first degree-granting historically black university.

Murphy, an Irish-Catholic transplant from Boston's commuter suburbs grew up lower middle class but graduated from Harvard University.

Murphy used his Harvard economics degree go on to make millions at Goldman Sachs.

Oliver took her masters in urban planning and administration she got from Columbia University and put to extensive use in Essex County, where she works as an assistant administrator.

She previously served on the East Orange Board of Education from 1994-2000 and as its president from 1999 to 2000.

In 1997, Oliver narrowly lost the Democratic mayoral primary in the City of East Orange, losing the election by a 51 votes to Robert L. Bowser, who served three terms.

Oliver also serves on both the Assembly's commerce and economic development committee and the Legislature's joint committee on and equal employment opportunity.

As a woman of color with a long track record of helping Jersey's urban communities, Oliver also could help Murphy connect his message of economic renewal to African American voters who may have cooled to Democratic politics in the post-Obama era.

Hillary Clinton won New Jersey by 14 points last year but President Obama carried the state by 17.7 points in 2012.

Exit polling data shows Clinton's failed 2016 presidential bid was informed by weaker turnout by black voters and stronger-than-expected turnout among white and Hispanic voters. New Jersey mirrored that trend.

The lowest voter turnout in 2016 was in Essex County, at 59 percent -- three and a half percentage points lower than in 2012, when Obama was reelected.

Essex is 42 percent white and 40 percent black.

Murphy had also reportedly closely considered Assemblywoman Shavonda Sumter (D-Passaic) for his running mate. Sumter is the goddaughter of state Democratic Party chairman John Currie, and been contemplating her own run for governor until Murphy emerged.

Both the Murphy campaign and Oliver declined to comment.

Recent polls show Murphy leading Lt. Gov. Kim Guadagno, the Republican nominee, by more than 20 percentage points in the race to succeed Gov. Chris Christie, a term-limited Republican in the final months of his last term.

Guadagno has not yet announced her running mate.

Claude Brodesser-Akner may be reached at cbrodesser@njadvancemedia.com. Follow him on Twitter @ClaudeBrodesser. Find NJ.com Politics on Facebook.