PolyMet Strengthens Finance Team; Patrick Keenan Appointed Chief Financial Officer; Douglas Newby to Focus on Project Finance

ST. PAUL, Minn.–(BUSINESS WIRE)–PolyMet Mining Corp. (TSX: POM) (NYSE MKT: PLM) (“PolyMet” or the
“Company”) today announced the appointment of Patrick Keenan as Chief
Financial Officer of PolyMet effective June 15, 2017. Mr. Keenan
succeeds Douglas Newby, who has served as CFO for nearly twelve years
through a period of great transition and progress for the Company. Mr.
Newby will continue to advise the Company as President of Proteus
Capital focusing on project finance and strategy.

“I am very pleased to welcome Pat to PolyMet as we enter the very
exciting and important phase of project finance and prepare to construct
the first copper-nickel-precious metals mine in Minnesota,” stated Jon
Cherry, President and CEO of PolyMet. “His strong financial background
and understanding of the mining industry, including his global
experience in a broad range of senior financial roles are an excellent
fit for the next stage of development at PolyMet.”

Mr. Keenan most recently served as Senior Vice President Finance and
Treasurer at Newmont. Prior to this he spent more than 20 years with Rio
Tinto in a variety of roles, including chief financial officer for Rio
Tinto’s Energy group and chief financial officer for Kennecott Utah
Copper and Rio Tinto Diamonds. Mr. Keenan earned his degree in
Accounting from the University of Utah and is a CPA.

“PolyMet has done an excellent job moving the NorthMet Project through
the EIS and permitting process over the last few years. It is an
exciting time to join the Company and I look forward to contributing to
the overall success and development of the first copper-nickel mine in
Minnesota,” said Pat Keenan.

Mr. Cherry added, “I would also like to express my sincere thanks and
appreciation for the nearly twelve years of dedicated service provided
by Douglas as CFO of PolyMet.”

During Mr. Newby’s tenure as a core team member, the Company completed
its Definitive Feasibility Study establishing reserves, acquired the
Erie Plant and associated infrastructure, entered into the strategic
alliance with Glencore, completed the final EIS, submitted all permit
applications and received the USFS Land Exchange Record of Decision. Mr.
Newby also oversaw Sarbanes Oxley compliance, adoption of IFRS, and
listing on the NYSE-MKT and TSX stock exchanges.

As President of Proteus Capital, Mr. Newby will continue to advise
PolyMet on project financing and strategy. Mr. Newby stated, “I am
excited with the advances PolyMet has made and pleased to maintain my
long-term involvement with and commitment to the project while handing
the reins to someone with Pat’s depth of experience.”

“We are very excited at PolyMet for the significant progress that has
been made to date and look forward to the release of draft air, water,
and mining permits for public review and comment. Likewise, we are
excited for the opportunity to grow our team and our company as we
prepare to finance and construct our project,” Mr. Cherry concluded.

About PolyMet
PolyMet Mining Corp. (www.polymetmining.com)
is a publicly traded mine development company that owns 100 percent of
Poly Met Mining, Inc., a Minnesota corporation that controls 100 percent
of the NorthMet copper-nickel-precious metals ore body through a
long-term lease and owns 100 percent of the Erie Plant, a large
processing facility located approximately six miles from the ore body in
the established mining district of the Mesabi Iron Range in northeastern
Minnesota. Poly Met Mining, Inc. has completed its Definitive
Feasibility Study. The NorthMet Final EIS was published in November
2015, preparing the way for decisions on permit applications. NorthMet
is expected to require approximately two million hours of construction
labor, create approximately 360 long-term jobs directly, and generate a
level of activity that will have a significant multiplier effect in the
local economy.

PolyMet Disclosures
This news release contains certain
forward-looking statements concerning anticipated developments in
PolyMet’s operations in the future. Forward-looking statements are
frequently, but not always, identified by words such as “expects,”
“anticipates,” “believes,” “intends,” “estimates,” “potential,”
“possible,” “projects,” “plans,” and similar expressions, or statements
that events, conditions or results “will,” “may,” “could,” or “should”
occur or be achieved or their negatives or other comparable words. These
forward-looking statements may include statements regarding the ability
to receive environmental and operating permits, job creation, and the
effect on the local economy, or other statements that are not a
statement of fact. Forward-looking statements address future events and
conditions and therefore involve inherent known and unknown risks and
uncertainties. Actual results may differ materially from those in the
forward-looking statements due to risks facing PolyMet or due to actual
facts differing from the assumptions underlying its predictions.

PolyMet’s forward-looking statements are based on the beliefs,
expectations and opinions of management on the date the statements are
made, and PolyMet does not assume any obligation to update
forward-looking statements if circumstances or management’s beliefs,
expectations and opinions should change.

Specific reference is made to PolyMet’s most recent Annual
Information Form for the fiscal year ended January 31, 2017 and in other
filings with Canadian securities authorities and the U.S. Securities and
Exchange Commission, including the Company’s Form 6-K providing
information with respect to operations for the three months ended April
30, 2017, for a discussion of some of the risk factors and other
considerations underlying forward-looking statements. The Annual
Information Form contains the Company’s mineral resource and other data
as required under National Instrument 43-101.

The TSX has not reviewed and does not accept responsibility for the
adequacy or accuracy of this release.

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Contacts

PolyMet Mining Corp.
Media
Bruce Richardson, +1
651-389-4111
Corporate Communications
[email protected]
or
Investor
Relations
Jenny Knudson, +1 651-389-4110
Investor Relations
[email protected]