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EXHIBIT 12.1

CERTIFICATION

I, Joseph Conway, certify that:

(1) I have reviewed this Annual Report on Form 20-F of Primero
Mining Corp. for the year ended December 31, 2017.

(2) Based on my knowledge, this report does not contain any
untrue statement of a material fact or omit to state a material fact necessary
to make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by this
report.

(3) Based on my knowledge, the financial statements, and other
financial information included in this report, fairly present in all material
respects the financial condition, results of operations and cash flows of the
issuer as of, and for, the periods presented in this report.

(4) The issuers other certifying officer(s) and I are
responsible for establishing and maintaining disclosure controls and procedures
(as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control
over financial reporting (as defined in Exchange Act Rules 13a-15(f) and
15d-15(f)) for the issuer and have:

(a) designed such disclosure controls
and procedures, or caused such disclosure controls and procedures to be designed
under our supervision, to ensure that material information relating to the
issuer, including its consolidated subsidiaries, is made known to us by others
within those entities, particularly during the period in which this report is
being prepared;

(b) designed such internal control over
financial reporting, or caused such internal control over financial reporting 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 generally accepted accounting
principles;

(c) evaluated the effectiveness of the
issuers disclosure controls and procedures and presented in this report our
conclusions about the effectiveness of the disclosure controls and procedures,
as of the end of the period covered by this report based on such evaluation; and

(d) disclosed in this report any change
in the issuers internal control over financial reporting that occurred during
the period covered by the annual report that has materially affected, or is
reasonably likely to materially affect, the issuers internal control over
financial reporting.

(5) The issuers other certifying officer(s) and I have
disclosed, based on our most recent evaluation of the internal control over
financial reporting, to the issuers independent registered public accounting
firm and the audit committee of issuers board of directors (or persons
performing the equivalent functions):

(a) all significant deficiencies and
material weaknesses in the design or operation of internal control over
financial reporting which are reasonably likely to adversely affect the issuers
ability to record, process, summarize and report financial information; and

(b) any fraud, whether or not material,
that involves management or other employees who have a significant role in the
issuers internal control over financial reporting.

Date: April 20, 2018

|By:    | /s/                                          
|------ | ---------------------------------------------
|Name:  | Joseph Conway                                
|Title: | Interim President and Chief Executive Officer

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