Exhibit 4



FORM 52-109F1

CERTIFICATION OF ANNUAL FILINGS



I, Craig Scherba, Chief Executive Officer of NextSource Materials
Inc., certify the following:



1. Review: I have reviewed the AIF, if any, annual
financial statements and annual MD&A, including, for greater certainty, all documents and information that are incorporated
by reference in the AIF (together, the “annual filings”) of NextSource Materials Inc. (the “issuer”) for
the financial year ended June 30, 2018.



2. No misrepresentations: Based on my knowledge, having
exercised reasonable diligence, the annual filings do not contain any untrue statement of a material fact or omit to state a material
fact required to be stated or that is necessary to make a statement not misleading in light of the circumstances under which it
was made, for the period covered by the annual filings.



3. Fair presentation: Based on my knowledge, having
exercised reasonable diligence, the annual financial statements together with the other financial information included in the annual
filings fairly present in all material respects the financial condition, results of operations and cash flows of the issuer, as
of the date of and for the periods presented in the annual filings.



4. Responsibility: The issuer’s other certifying
officer and I are responsible for establishing and maintaining disclosure controls and procedures (DC&P) and internal control
over financial reporting (ICFR), as those terms are defined in National Instrument 52-109 Certification of Disclosure in Issuers’
Annual and Interim Filings, for the issuer.



5. Design: Subject to the limitations, if any, described
in paragraphs 5.2 and 5.3, the issuer’s other certifying officer and I have, as at the financial year end:



| | a. | designed DC&P, or caused it to be designed under our supervision, to provide reasonable assurance
that
| | -- | ------------------------------------------------------------------------------------------------------



| | i. | material information relating to the issuer is made known to us by others, particularly during
the period in which the annual filings are being prepared; and
| | -- | -------------------------------------------------------------------------------------------------------------------------------------------------------------



| | ii. | information required to be disclosed by the issuer in its annual filings, interim filings or other
reports filed or submitted by it under securities legislation is recorded, processed, summarized and reported within the time periods
specified in securities legislation; and
| | --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | b. | designed ICFR, or caused it to be designed under our supervision, to provide reasonable assurance
regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance
with the issuer’s GAAP.
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



5.1 Control framework: The control framework the issuer’s
other certifying officer and I used to design the issuer’s ICFR is the Internal Control – Integrated Framework (2013
COSO Framework) published by The Committee of Sponsoring Organizations.



5.2 ICFR – material weakness relating to design:N/A



5.3 Limitation of scope of design:N/A



6. Evaluation: The issuer’s other certifying officer and I have:



| | a. | evaluated, or caused to be evaluated under our supervision, the effectiveness of the issuer’s
DC&P at the financial year end and the issuer has disclosed in its annual MD&A our conclusions about the effectiveness
of DC&P at the financial year end based on that evaluation; and
| | -- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | b. | evaluated, or caused to be evaluated under our supervision, the effectiveness of the issuer’s
ICFR at the financial year end and the issuer has disclosed in its annual MD&A
| | -- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| | i. | our conclusions about the effectiveness of ICFR at the financial year end based on that evaluation;
and
| | -- | -------------------------------------------------------------------------------------------------------



| | ii. | N/A
| | --- | ---



7. Reporting changes in ICFR: The issuer has disclosed
in its annual MD&A any change in the issuer’s ICFR that occurred during the period beginning on April 1, 2018
and ended on June 30, 2018 that has materially affected, or is reasonably likely to materially affect, the issuer’s
ICFR.



8. Reporting to the issuer’s auditors and board of directors
or audit committee: The issuer’s other certifying officer(s) and I have disclosed, based on our most recent evaluation
of ICFR, to the issuer’s auditors, and the board of directors or the audit committee of the board of directors any fraud
that involves management or other employees who have a significant role in the issuer’s ICFR.



Date: September 28, 2018



/s/ Craig Scherba

Craig Scherba

Chief Executive Officer