diff --git a/src/ekp_interface.jl b/src/ekp_interface.jl
index 7025183b..c6fc9ef8 100644
--- a/src/ekp_interface.jl
+++ b/src/ekp_interface.jl
@@ -190,12 +190,17 @@ end
 """
     initialize(ensemble_size, observations, noise, prior, output_dir; kwargs...)
     initialize(ensemble_size, observations, prior, output_dir; kwargs...)
+    initialize(eki::EnsembleKalmanProcess, prior, output_dir)
     initialize(config::ExperimentConfig; kwargs...)
     initialize(filepath::AbstractString; kwargs...)
 
 Initialize the EnsembleKalmanProcess object and parameter files.
 
+Can take in an existing EnsembleKalmanProcess which will be used to generate the
+ initial parameter ensemble.
+
 Noise is optional when the observation is an EKP.ObservationSeries.
+
 Additional kwargs may be passed through to the EnsembleKalmanProcess constructor.
 """
 initialize(filepath::AbstractString; kwargs...) =
@@ -244,6 +249,11 @@ initialize(
     ekp_kwargs...,
 )
 
+function initialize(eki::EKP.EnsembleKalmanProcess, prior, output_dir)
+    save_eki_state(eki, output_dir, 0, prior)
+    return eki
+end
+
 function _initialize(
     ensemble_size,
     observations,
diff --git a/test/ekp_interface.jl b/test/ekp_interface.jl
index b90a1b93..02beb55f 100644
--- a/test/ekp_interface.jl
+++ b/test/ekp_interface.jl
@@ -5,6 +5,11 @@ import ClimaCalibrate as CAL
 import ClimaParams as CP
 import LinearAlgebra: I
 using Test
+import Random
+
+rng_seed = 1234
+Random.seed!(rng_seed)
+rng_ekp = Random.MersenneTwister(rng_seed)
 
 FT = Float64
 output_dir = "test_init"
@@ -56,6 +61,30 @@ params = CP.get_parameter_values(td, param_names)
     @test params.two == 5.408386812503563
 end
 
+@testset "Test passing an EKP struct into `initialize`" begin
+    LHF_target = 4.0
+    ensemble_size = 5
+    N_iterations = 5
+    Γ = 20.0 * EKP.I
+    output_dir = joinpath("test", "custom_ekp")
+    initial_ensemble =
+        EKP.construct_initial_ensemble(rng_ekp, prior, ensemble_size)
+    ensemble_kalman_process = EKP.EnsembleKalmanProcess(
+        initial_ensemble,
+        LHF_target,
+        Γ,
+        EKP.Inversion(),
+    )
+    CAL.initialize(ensemble_kalman_process, prior, output_dir)
+    override_file =
+        joinpath(output_dir, "iteration_000", "member_001", "parameters.toml")
+    td = CP.create_toml_dict(FT; override_file)
+    params = CP.get_parameter_values(td, param_names)
+    @test params.one == 4.506555276137722
+    @test params.two == 5.408386812503563
+end
+
+
 @testset "Environment variables" begin
     @test_throws ErrorException(
         "Experiment dir not found in environment. Ensure that env variable \"CALIBRATION_EXPERIMENT_DIR\" is set.",